feat: support TypeScript 4.0 (#1889)

Author: ahnpnl

e2e/__external-repos__/custom-typings/package.json

@@ -5,11 +5,11 @@
     "test": "jest"
   },
   "devDependencies": {
-    "@types/jest": "^26.0.9",
+    "@types/jest": "^26.0.10",
     "@types/jquery": "^3.5.1",
-    "jest": "^26.3.0",
+    "jest": "^26.4.1",
     "jquery": "^3.5.1",
-    "typescript": "^3.9.7"
+    "typescript": "^4.0.2"
   },
   "wantedDependencies": {
     "jquery": "latest",