chore(package): update mocha to version 4.1.0

Closes #22

Author: greenkeeper[bot]

package.json

@@ -32,6 +32,6 @@
     "coveralls": "^2.11.9",
     "eslint": "^3.0.0",
     "istanbul": "^0.4.3",
-    "mocha": "^3.0.2"
+    "mocha": "^4.1.0"
   }
 }