chore(package): update gulp-mocha to version 4.1.0

Closes #20

https://greenkeeper.io/

Author: greenkeeper[bot]

package.json

@@ -38,6 +38,6 @@
     "eslint": "^3.11.1",
     "gulp": "^3.9.1",
     "gulp-eslint": "^3.0.1",
-    "gulp-mocha": "^3.0.1"
+    "gulp-mocha": "^4.1.0"
   }
 }