Bump bootstrap from 4.1.3 to 4.2.1
Bump bootstrap from 4.1.3 to 4.2.1

Bumps [bootstrap](https://github.com/twbs/bootstrap) from 4.1.3 to 4.2.1.
- [Release notes](https://github.com/twbs/bootstrap/releases)
- [Commits](https://github.com/twbs/bootstrap/compare/v4.1.3...v4.2.1)

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