Update dependency webpack to v4

Author: renovate-bot

packages/Site/package.json

@@ -23,7 +23,7 @@
     "cross-env": "5.1.4",
     "nodemon": "1.17.3",
     "typescript": "2.7.1",
-    "webpack": "3.11.0"
+    "webpack": "4.8.0"
   },
   "dependencies": {
     "@slup/buttons": "^0.5.0",