Bump jsonwebtoken from 8.4.0 to 9.0.0 in /backend

Bumps [jsonwebtoken](https://github.com/auth0/node-jsonwebtoken) from 8.4.0 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@v8.4.0...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

@@ -18,7 +18,7 @@
     "dotenv": "^6.2.0",
     "express": "^4.16.4",
     "fs": "0.0.1-security",
-    "jsonwebtoken": "^8.4.0",
+    "jsonwebtoken": "^9.0.0",
     "lodash": "^4.17.19",
     "mongoose": "^5.7.11",
     "multer": "^1.4.1",