build(deps-dev): bump mocha from 6.2.0 to 6.2.1

Bumps [mocha](https://github.com/mochajs/mocha) from 6.2.0 to 6.2.1.
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/v6.2.1/CHANGELOG.md)
- [Commits](mochajs/mocha@v6.2.0...v6.2.1)

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