upgrade to the latest webpack-dev-server

Author: heygrady

packages/react-scripts/package.json

@@ -77,7 +77,7 @@
     "ts-pnp": "1.1.4",
     "url-loader": "2.2.0",
     "webpack": "4.41.2",
-    "webpack-dev-server": "3.2.1",
+    "webpack-dev-server": "3.9.0",
     "webpack-manifest-plugin": "2.2.0",
     "workbox-webpack-plugin": "4.3.1"
   },