chore(package): update mocha to version 4.0.0 (#17)

Author: greenkeeper[bot]

package.json

@@ -25,7 +25,7 @@
   "devDependencies": {
     "coveralls": "^3.0.0",
     "istanbul": "^0.4.5",
-    "mocha": "^3.0.2",
+    "mocha": "^4.0.0",
     "should": "^13.0.0"
   }
 }