Bump eventlet from 0.27.0 to 0.28.0 in /backend/uclapi
Bump eventlet from 0.27.0 to 0.28.0 in /backend/uclapi

Bumps [eventlet](https://github.com/eventlet/eventlet) from 0.27.0 to 0.28.0.
- [Release notes](https://github.com/eventlet/eventlet/releases)
- [Changelog](https://github.com/eventlet/eventlet/blob/master/NEWS)
- [Commits](https://github.com/eventlet/eventlet/compare/v0.27.0...v0.28.0)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
uclapi/uclapi,uclapi/uclapi,uclapi/uclapi,uclapi/uclapi