Update dependency webpack-dev-server to v3

Author: WhiteSource for github.com

package.json

@@ -52,7 +52,7 @@
     "raphael": "^2.1.0",
     "slimerjs": "^0.906.2",
     "webpack": "*",
-    "webpack-dev-server": "^1.14.1"
+    "webpack-dev-server": "^3.1.6"
   },
   "scripts": {
     "start": "grunt stage",