Update immer dependency for website

CRA is still in the process of updating with the immer fix
( facebook/create-react-app#10412 ), so this uses a
resolution override to use the newest immer. To reduce chance of compatibility
issues, I also updated `react-dev-utils` to latest and confirmed that dev and
prod builds both still work.

website/package.json

@@ -31,7 +31,7 @@
     "object-assign": "^4.1.1",
     "promise": "^8.0.3",
     "react": "^16.11.0",
-    "react-dev-utils": "^9.1.0",
+    "react-dev-utils": "^11.0.1",
     "react-dom": "^16.11.0",
     "react-hot-loader": "^4.12.16",
     "react-monaco-editor": "^0.32.1",
@@ -52,7 +52,8 @@
     "publish-website": "scripts/publish.sh"
   },
   "resolutions": {
-    "**/@types/react": "16.14.2"
+    "**/@types/react": "16.14.2",
+    "**/immer": "8.0.1"
   },
   "jest": {
     "collectCoverageFrom": [