build: bump prettier from 1.8.2 to 1.12.1

Bumps [prettier](https://github.com/prettier/prettier) from 1.8.2 to 1.12.1.
- [Release notes](https://github.com/prettier/prettier/releases)
- [Changelog](https://github.com/prettier/prettier/blob/master/CHANGELOG.md)
- [Commits](prettier/prettier@1.8.2...1.12.1)

Signed-off-by: dependabot[bot] <support@dependabot.com>