chore(package): update mocha to version 6.1.0

Closes #5

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
     "coveralls": "^3.0.0",
     "eslint": "^4.4.1",
     "js-promisify": "^1.1.0",
-    "mocha": "^4.0.0",
+    "mocha": "^6.1.0",
     "nyc": "^11.1.0",
     "rimraf": "^2.6.1",
     "webpack": "^3.5.4",