Update dependency webpack-cli to v4

Author: renovate-bot

package.json

@@ -46,7 +46,7 @@
     "jest": "24.9.0",
     "webpack": "4.41.2",
     "jsdom": "15.2.0",
-    "webpack-cli": "3.3.9"
+    "webpack-cli": "4.7.2"
   },
   "dependencies": {}
 }