chore(package): update webpack to version 2.5.1

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -71,7 +71,7 @@
     "stylus-loader": "2.3.1",
     "testdouble": "^1.4.2",
     "url-loader": "0.5.7",
-    "webpack": "1.13.2",
+    "webpack": "2.5.1",
     "webpack-dev-server": "1.16.1"
   },
   "engines": {