Update autoprefixer requirement from 9.4.0 to 9.4.2 (#18)
Update autoprefixer requirement from 9.4.0 to 9.4.2 (#18)

Updates the requirements on [autoprefixer](https://github.com/postcss/autoprefixer) to permit the latest version.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/autoprefixer/commits/9.4.2)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
hexojs/hexo-autoprefixer