Bump bootstrap in /public/js/lib/bootstrap-material-design

Bumps [bootstrap](https://github.com/twbs/bootstrap) from 4.1.1 to 4.3.1.
- [Release notes](https://github.com/twbs/bootstrap/releases)
- [Commits](twbs/bootstrap@v4.1.1...v4.3.1)

---
updated-dependencies:
- dependency-name: bootstrap
  dependency-type: direct:production
...

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Author: dependabot[bot]