Update webpack-dev-server 3.1.9 -> 3.1.14 (#6064)

* Update webpack-dev-server 3.1.9 -> 3.1.14

Author: Friss

Diff for: packages/react-scripts/package.json

@@ -68,7 +68,7 @@
     "terser-webpack-plugin": "1.1.0",
     "url-loader": "1.1.1",
     "webpack": "4.19.1",
-    "webpack-dev-server": "3.1.9",
+    "webpack-dev-server": "3.1.14",
     "webpack-manifest-plugin": "2.0.4",
     "workbox-webpack-plugin": "3.6.3"
   },