build: update webpack-dev-server to version 3.4.1

Author: renovate-bot

packages/angular_devkit/build_angular/package.json

@@ -50,7 +50,7 @@
     "terser-webpack-plugin": "1.2.4",
     "webpack": "4.31.0",
     "webpack-dev-middleware": "3.7.0",
-    "webpack-dev-server": "3.3.1",
+    "webpack-dev-server": "3.4.1",
     "webpack-merge": "4.2.1",
     "webpack-sources": "1.3.0",
     "webpack-subresource-integrity": "1.1.0-rc.6",