Bump vendor/github.com/twbs/bootstrap-rubygem

Bumps [vendor/github.com/twbs/bootstrap-rubygem](https://github.com/twbs/bootstrap-rubygem) from `ce9dfc2` to `1e6b6b2`.
- [Release notes](https://github.com/twbs/bootstrap-rubygem/releases)
- [Commits](twbs/bootstrap-rubygem@ce9dfc2...1e6b6b2)

---
updated-dependencies:
- dependency-name: vendor/github.com/twbs/bootstrap-rubygem
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>