Bump bootstrap from 4.5.3 to 4.6.0

Bumps [bootstrap](https://github.com/twbs/bootstrap) from 4.5.3 to 4.6.0.
- [Release notes](https://github.com/twbs/bootstrap/releases)
- [Commits](https://github.com/twbs/bootstrap/compare/v4.5.3...v4.6.0

)

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