chore(package): update webpack to version 1.13.1

https://greenkeeper.io/

package.json

@@ -201,7 +201,7 @@
     "style-loader": "0.13.1",
     "supertest": "1.2.0",
     "supertest-as-promised": "3.0.0",
-    "webpack": "1.13.0",
+    "webpack": "1.13.1",
     "webpack-dev-middleware": "1.6.1",
     "webpack-dev-server": "1.14.1",
     "webpack-hot-middleware": "2.10.0",