fix(package): update webpack-dev-middleware to version 2.0.0

Closes #59

Author: greenkeeper[bot]

package.json

@@ -51,7 +51,7 @@
     ]
   },
   "dependencies": {
-    "webpack-dev-middleware": "1.12.0",
+    "webpack-dev-middleware": "2.0.0",
     "webpack-hot-middleware": "2.18.2",
     "regenerator-runtime": "0.10.5"
   }