fix: upgrade express from 4.13.4 to 4.21.1

Snyk has created this PR to upgrade express from 4.13.4 to 4.21.1.

See this package in npm:
express

See this project in Snyk:
https://app.snyk.io/org/sammytezzy/project/5808f7c2-f381-4376-abdf-a051396521a3?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot

examples/cluster-nginx/server/package.json

@@ -8,7 +8,7 @@
   "license": "MIT",
   "dependencies": {
     "@socket.io/redis-adapter": "^7.0.1",
-    "express": "4.13.4",
+    "express": "4.21.1",
     "redis": "^3.1.2",
     "socket.io": "^4.0.0"
   },