Bump omniauth-cas from 1.1.1 to 2.0.0 (#15165)

Bumps [omniauth-cas](https://github.com/dlindahl/omniauth-cas) from 1.1.1 to 2.0.0.
- [Release notes](https://github.com/dlindahl/omniauth-cas/releases)
- [Changelog](https://github.com/dlindahl/omniauth-cas/blob/master/CHANGELOG.md)
- [Commits](https://github.com/dlindahl/omniauth-cas/compare/v1.1.1...v2.0.0

)

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