Update dependency webpack-dev-server to v3.8.0

Author: renovate-bot

example/package.json

@@ -14,6 +14,6 @@
     "style-loader": "0.20.3",
     "webpack": "4.5.0",
     "webpack-cli": "2.0.14",
-    "webpack-dev-server": "3.1.3"
+    "webpack-dev-server": "3.8.0"
   }
 }