diff --git a/package-lock.json b/package-lock.json
index 8836923..323da4f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -645,12 +645,20 @@
             }
         },
         "clean-css": {
-            "version": "4.1.11",
-            "resolved": "https://registry.npmjs.org/clean-css/-/clean-css-4.1.11.tgz",
-            "integrity": "sha1-Ls3xRaujj1R0DybO/Q/z4D4SXWo=",
+            "version": "4.2.1",
+            "resolved": "https://registry.npmjs.org/clean-css/-/clean-css-4.2.1.tgz",
+            "integrity": "sha512-4ZxI6dy4lrY6FHzfiy1aEOXgu4LIsW2MhwG0VBKdcoGoH/XLFgaHSdLTGr4O8Be6A8r3MOphEiI8Gc1n0ecf3g==",
             "dev": true,
             "requires": {
-                "source-map": "0.5.7"
+                "source-map": "~0.6.0"
+            },
+            "dependencies": {
+                "source-map": {
+                    "version": "0.6.1",
+                    "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",
+                    "integrity": "sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==",
+                    "dev": true
+                }
             }
         },
         "cliui": {
@@ -1771,7 +1779,8 @@
                 "ansi-regex": {
                     "version": "2.1.1",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 },
                 "aproba": {
                     "version": "1.2.0",
@@ -1792,12 +1801,14 @@
                 "balanced-match": {
                     "version": "1.0.0",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 },
                 "brace-expansion": {
                     "version": "1.1.11",
                     "bundled": true,
                     "dev": true,
+                    "optional": true,
                     "requires": {
                         "balanced-match": "1.0.0",
                         "concat-map": "0.0.1"
@@ -1812,17 +1823,20 @@
                 "code-point-at": {
                     "version": "1.1.0",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 },
                 "concat-map": {
                     "version": "0.0.1",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 },
                 "console-control-strings": {
                     "version": "1.1.0",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 },
                 "core-util-is": {
                     "version": "1.0.2",
@@ -1939,7 +1953,8 @@
                 "inherits": {
                     "version": "2.0.3",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 },
                 "ini": {
                     "version": "1.3.5",
@@ -1951,6 +1966,7 @@
                     "version": "1.0.0",
                     "bundled": true,
                     "dev": true,
+                    "optional": true,
                     "requires": {
                         "number-is-nan": "1.0.1"
                     }
@@ -1965,6 +1981,7 @@
                     "version": "3.0.4",
                     "bundled": true,
                     "dev": true,
+                    "optional": true,
                     "requires": {
                         "brace-expansion": "1.1.11"
                     }
@@ -1972,12 +1989,14 @@
                 "minimist": {
                     "version": "0.0.8",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 },
                 "minipass": {
                     "version": "2.2.4",
                     "bundled": true,
                     "dev": true,
+                    "optional": true,
                     "requires": {
                         "safe-buffer": "5.1.1",
                         "yallist": "3.0.2"
@@ -1996,6 +2015,7 @@
                     "version": "0.5.1",
                     "bundled": true,
                     "dev": true,
+                    "optional": true,
                     "requires": {
                         "minimist": "0.0.8"
                     }
@@ -2076,7 +2096,8 @@
                 "number-is-nan": {
                     "version": "1.0.1",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 },
                 "object-assign": {
                     "version": "4.1.1",
@@ -2088,6 +2109,7 @@
                     "version": "1.4.0",
                     "bundled": true,
                     "dev": true,
+                    "optional": true,
                     "requires": {
                         "wrappy": "1.0.2"
                     }
@@ -2173,7 +2195,8 @@
                 "safe-buffer": {
                     "version": "5.1.1",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 },
                 "safer-buffer": {
                     "version": "2.1.2",
@@ -2209,6 +2232,7 @@
                     "version": "1.0.2",
                     "bundled": true,
                     "dev": true,
+                    "optional": true,
                     "requires": {
                         "code-point-at": "1.1.0",
                         "is-fullwidth-code-point": "1.0.0",
@@ -2228,6 +2252,7 @@
                     "version": "3.0.1",
                     "bundled": true,
                     "dev": true,
+                    "optional": true,
                     "requires": {
                         "ansi-regex": "2.1.1"
                     }
@@ -2271,12 +2296,14 @@
                 "wrappy": {
                     "version": "1.0.2",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 },
                 "yallist": {
                     "version": "3.0.2",
                     "bundled": true,
-                    "dev": true
+                    "dev": true,
+                    "optional": true
                 }
             }
         },
@@ -2605,15 +2632,26 @@
             }
         },
         "gulp-clean-css": {
-            "version": "3.9.4",
-            "resolved": "https://registry.npmjs.org/gulp-clean-css/-/gulp-clean-css-3.9.4.tgz",
-            "integrity": "sha512-jsbAj65WM08H1jCFOKpIvA1OlACk7OHS2FFTeeBZrSJ5OR1PJzAqi0I2R2LTWYN3oMd/N1JYN9cN2IS/8eYqdg==",
+            "version": "4.2.0",
+            "resolved": "https://registry.npmjs.org/gulp-clean-css/-/gulp-clean-css-4.2.0.tgz",
+            "integrity": "sha512-r4zQsSOAK2UYUL/ipkAVCTRg/2CLZ2A+oPVORopBximRksJ6qy3EX1KGrIWT4ZrHxz3Hlobb1yyJtqiut7DNjA==",
             "dev": true,
             "requires": {
-                "clean-css": "4.1.11",
+                "clean-css": "4.2.1",
                 "plugin-error": "1.0.1",
-                "through2": "2.0.3",
+                "through2": "3.0.1",
                 "vinyl-sourcemaps-apply": "0.2.1"
+            },
+            "dependencies": {
+                "through2": {
+                    "version": "3.0.1",
+                    "resolved": "https://registry.npmjs.org/through2/-/through2-3.0.1.tgz",
+                    "integrity": "sha512-M96dvTalPT3YbYLaKaCuwu+j06D/8Jfib0o/PxbVt6Amhv3dUAtW6rTV1jPgJSBG83I/e04Y6xkVdVhSRhi0ww==",
+                    "dev": true,
+                    "requires": {
+                        "readable-stream": "2 || 3"
+                    }
+                }
             }
         },
         "gulp-header": {
diff --git a/package.json b/package.json
index 8594b05..79673ea 100644
--- a/package.json
+++ b/package.json
@@ -38,7 +38,7 @@
     "devDependencies": {
         "browser-sync": "2.24.5",
         "gulp": "^3.9.1",
-        "gulp-clean-css": "3.9.4",
+        "gulp-clean-css": "4.2.0",
         "gulp-header": "2.0.5",
         "gulp-rename": "1.3.0",
         "gulp-sass": "4.0.1",