fix(package): update debug to version 4.0.0

Closes #29

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
   },
   "dependencies": {
     "bluebird": "^3.5.0",
-    "debug": "^2.6.8",
+    "debug": "^4.0.0",
     "lodash": "^4.17.4"
   },
   "peerDependencies": {