Bump knex from 0.20.15 to 2.4.0 in /backend

Bumps [knex](https://github.com/knex/knex) from 0.20.15 to 2.4.0.
- [Release notes](https://github.com/knex/knex/releases)
- [Changelog](https://github.com/knex/knex/blob/master/CHANGELOG.md)
- [Commits](https://github.com/knex/knex/compare/0.20.15...2.4.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

backend/package.json

@@ -16,7 +16,7 @@
 		"gravatar": "^1.8.0",
 		"json-schema-ref-parser": "^8.0.0",
 		"jsonwebtoken": "^8.5.1",
-		"knex": "^0.20.13",
+		"knex": "^2.4.0",
 		"liquidjs": "^9.11.10",
 		"lodash": "^4.17.21",
 		"moment": "^2.29.4",