fix: upgrade posthog-node from 2.1.0 to 2.2.0

Snyk has created this PR to upgrade posthog-node from 2.1.0 to 2.2.0.

See this package in npm:
https://www.npmjs.com/package/posthog-node

See this project in Snyk:
https://app.snyk.io/org/maidul98/project/35057e82-ed7d-4e19-ba4d-719a42135cd6?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot

backend/package-lock.json

@@ -19,7 +19,7 @@
     "jsrp": "^0.2.4",
     "mongoose": "^6.7.2",
     "nodemailer": "^6.8.0",
-    "posthog-node": "^2.1.0",
+    "posthog-node": "^2.2.0",
     "query-string": "^7.1.3",
     "rimraf": "^3.0.2",
     "stripe": "^10.7.0",