chore(deps): update dependency webpack-dev-server to v3 [security]

Author: renovate-bot

package.json

@@ -48,7 +48,7 @@
     "source-map-loader": "^0.2.1",
     "url-loader": "^0.6.2",
     "webpack": "^3.0.0",
-    "webpack-dev-server": "^2.11.1",
+    "webpack-dev-server": "^3.0.0",
     "webpack-node-externals": "^1.6.0"
   },
   "homepage": "https://identity.netlify.com",