chore(package): update mocha to version 4.0.0

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
     "loader-utils": "^1.0.4"
   },
   "devDependencies": {
-    "mocha": "^3.0.0",
+    "mocha": "^4.0.0",
     "safe-buffer": "^5.0.1",
     "standard": "^10.0.1"
   },