build(deps-dev): bump tailwindcss from 2.0.4 to 2.1.1 in /docs

Bumps [tailwindcss](https://github.com/tailwindlabs/tailwindcss) from 2.0.4 to 2.1.1.
- [Release notes](https://github.com/tailwindlabs/tailwindcss/releases)
- [Changelog](https://github.com/tailwindlabs/tailwindcss/blob/master/CHANGELOG.md)
- [Commits](tailwindlabs/tailwindcss@v2.0.4...v2.1.1)

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

Author: dependabot[bot]