chore(package): update mocha to version 4.1.0

Closes #39

Author: greenkeeper[bot]

package.json

@@ -10,7 +10,7 @@
     "coveralls": "^2.11.6",
     "expect.js": "^0.3.1",
     "istanbul": "^0.4.1",
-    "mocha": "^3.0.2"
+    "mocha": "^4.1.0"
   },
   "scripts": {
     "test": "mocha --bail",