chore(package): update mocha to version 4.0.0

Author: greenkeeper[bot]

package.json

@@ -28,6 +28,6 @@
   "devDependencies": {
     "chai": "^4.0.2",
     "istanbul": "^0.4.5",
-    "mocha": "^3.3.0"
+    "mocha": "^4.0.0"
   }
 }