Update dependency webpack-dev-server to v3.9.0

Author: renovate-bot

package-lock.json

@@ -84,7 +84,7 @@
     "ts-pnp": "1.1.4",
     "url-loader": "2.1.0",
     "webpack": "4.41.2",
-    "webpack-dev-server": "3.2.1",
+    "webpack-dev-server": "3.9.0",
     "webpack-manifest-plugin": "2.1.1",
     "workbox-webpack-plugin": "4.3.1"
   },