chore(deps-dev): bump @typescript-eslint/eslint-plugin

Bumps [@typescript-eslint/eslint-plugin](https://github.com/typescript-eslint/typescript-eslint/tree/HEAD/packages/eslint-plugin) from 2.20.0 to 2.21.0.
- [Release notes](https://github.com/typescript-eslint/typescript-eslint/releases)
- [Changelog](https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/CHANGELOG.md)
- [Commits](https://github.com/typescript-eslint/typescript-eslint/commits/v2.21.0/packages/eslint-plugin)

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