fix: plugins/rollbar-backend/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-BODYPARSER-7926860
- https://snyk.io/vuln/SNYK-JS-EXPRESS-7926867
- https://snyk.io/vuln/SNYK-JS-SEND-7926862
- https://snyk.io/vuln/SNYK-JS-SERVESTATIC-7926865

plugins/rollbar-backend/package.json

@@ -37,7 +37,7 @@
     "camelcase-keys": "^6.2.2",
     "compression": "^1.7.4",
     "cors": "^2.8.5",
-    "express": "^4.17.1",
+    "express": "^4.20.0",
     "express-promise-router": "^4.1.0",
     "fs-extra": "9.1.0",
     "helmet": "^4.0.0",