Bumps [bootstrap](https://github.com/twbs/bootstrap-rubygem) from 4.3.1 to 4.4.1.
- [Release notes](https://github.com/twbs/bootstrap-rubygem/releases)
- [Changelog](https://github.com/twbs/bootstrap-rubygem/blob/master/CHANGELOG.md)
- [Commits](https://github.com/twbs/bootstrap-rubygem/compare/v4.3.1...v4.4.1)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>