Bump slab from 0.4.1 to 0.4.2
Bump slab from 0.4.1 to 0.4.2

Bumps [slab](https://github.com/carllerche/slab) from 0.4.1 to 0.4.2.
- [Release notes](https://github.com/carllerche/slab/releases)
- [Changelog](https://github.com/carllerche/slab/blob/master/CHANGELOG.md)
- [Commits](https://github.com/carllerche/slab/compare/v0.4.1...v0.4.2)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
KiChjang/servo,KiChjang/servo,splav/servo,KiChjang/servo,KiChjang/servo,splav/servo,splav/servo,splav/servo,KiChjang/servo,splav/servo,KiChjang/servo,KiChjang/servo,splav/servo,KiChjang/servo,splav/servo,KiChjang/servo,splav/servo,KiChjang/servo,splav/servo,splav/servo