Bump grunt-stylelint from 0.16.0 to 0.18.0

Bumps [grunt-stylelint](https://github.com/wikimedia/grunt-stylelint) from 0.16.0 to 0.18.0.
- [Release notes](https://github.com/wikimedia/grunt-stylelint/releases)
- [Changelog](https://github.com/wikimedia/grunt-stylelint/blob/master/History.md)
- [Commits](wikimedia/grunt-stylelint@v0.16.0...v0.18.0)

---
updated-dependencies:
- dependency-name: grunt-stylelint
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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