chore(package): update mocha to version 3.1.2

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -37,7 +37,7 @@
     "docpress-core": "github:docpress/docpress-core",
     "expect": "1.20.2",
     "metalsmith": "2.2.0",
-    "mocha": "3.1.0",
+    "mocha": "3.1.2",
     "mocha-clean": "1.0.0",
     "nyc": "8.3.0",
     "standard": "8.3.0",