chore(package): update mocha to version 4.1.0

Closes #13

package.json

@@ -33,7 +33,7 @@
   "devDependencies": {
     "assume": "~1.5.0",
     "istanbul": "0.4.x",
-    "mocha": "~3.5.0",
+    "mocha": "~4.1.0",
     "pre-commit": "~1.2.0"
   }
 }