chore(package): update webpack-dev-server to version 3.1.2

Closes #45

Author: greenkeeper[bot]

package.json

@@ -63,7 +63,7 @@
     "style-loader": "^0.16.0",
     "url-loader": "^0.5.7",
     "webpack": "^1.13.1",
-    "webpack-dev-server": "^2.4.1",
+    "webpack-dev-server": "^3.1.2",
     "xo": "^0.19.0"
   },
   "dependencies": {