Maintenance: Bump messagebird-rest from 2.0.0 to 3.0.0
Bumps [messagebird-rest](https://github.com/messagebird/ruby-rest-api) from 2.0.0 to 3.0.0.
- [Release notes](https://github.com/messagebird/ruby-rest-api/releases)
- [Commits](https://github.com/messagebird/ruby-rest-api/compare/v2.0.0...3.0.0)