Merge pull request #956 from mozilla/greenkeeper-webpack-dev-server-1.15.0

Update webpack-dev-server to version 1.15.0 🚀

Author: muffinresearch

package.json

@@ -233,7 +233,7 @@
     "svg-url-loader": "1.1.0",
     "webpack": "1.13.2",
     "webpack-dev-middleware": "1.6.1",
-    "webpack-dev-server": "1.14.1",
+    "webpack-dev-server": "1.15.0",
     "webpack-hot-middleware": "2.12.2"
   }
 }