chore(package): update mocha to version 3.1.2

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -45,6 +45,6 @@
     "codecov.io": "^0.1.2",
     "coveralls": "^2.11.2",
     "eslint": "^1.5.0",
-    "mocha": "^2.2.5"
+    "mocha": "^3.1.2"
   }
 }