fix: upgrade express-rate-limit from 5.4.0 to 5.4.1

Snyk has created this PR to upgrade express-rate-limit from 5.4.0 to 5.4.1.

See this package in npm:
https://www.npmjs.com/package/express-rate-limit

See this project in Snyk:
https://app.snyk.io/org/johnmclear/project/d9a12bfb-7ccd-443f-9e22-f30d339cc8c5?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot

src/package-lock.json

@@ -39,7 +39,7 @@
     "etherpad-require-kernel": "^1.0.15",
     "etherpad-yajsml": "0.0.12",
     "express": "4.17.1",
-    "express-rate-limit": "5.4.0",
+    "express-rate-limit": "5.4.1",
     "express-session": "1.17.2",
     "fast-deep-equal": "^3.1.3",
     "find-root": "1.1.0",