chore(package): update mocha to version 3.1.0

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -28,7 +28,7 @@
     "expect": "1.20.2",
     "istanbul": "0.4.5",
     "metalsmith": "2.2.0",
-    "mocha": "3.0.2",
+    "mocha": "3.1.0",
     "mocha-clean": "1.0.0",
     "mocha-standard": "1.0.0",
     "standard": "8.3.0",