fix(package): update webpack-dev-server to version 3.2.1

Author: greenkeeper[bot]

package.json

@@ -82,7 +82,7 @@
     "update-notifier": "2.5.0",
     "validate-npm-package-name": "3.0.0",
     "webpack": "4.29.5",
-    "webpack-dev-server": "3.2.0",
+    "webpack-dev-server": "3.2.1",
     "webpack-merge": "4.2.1",
     "which": "1.3.1",
     "workbox-webpack-plugin": "3.6.3",