Bump jsonwebtoken from 8.5.1 to 9.0.0 in /backend

Bumps [jsonwebtoken](https://github.com/auth0/node-jsonwebtoken) from 8.5.1 to 9.0.0.
- [Release notes](https://github.com/auth0/node-jsonwebtoken/releases)
- [Changelog](https://github.com/auth0/node-jsonwebtoken/blob/master/CHANGELOG.md)
- [Commits](auth0/node-jsonwebtoken@v8.5.1...v9.0.0)

---
updated-dependencies:
- dependency-name: jsonwebtoken
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backend/package-lock.json

@@ -24,7 +24,7 @@
     "cors": "^2.8.5",
     "dotenv": "^8.2.0",
     "express": "^4.16.2",
-    "jsonwebtoken": "^8.5.1",
+    "jsonwebtoken": "^9.0.0",
     "lodash": "^4.17.20",
     "mongoose": "^5.11.9"
   }