build(deps-dev): bump black from 20.8b1 to 21.4b2 (#291)

Bumps [black](https://github.com/psf/black) from 20.8b1 to 21.4b2.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/master/CHANGES.md)
- [Commits](https://github.com/psf/black/commits)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>
Co-authored-by: Xavi Moreno <xaviml.93@gmail.com>

Pipfile

@@ -4,7 +4,7 @@ url = "https://pypi.org/simple"
 verify_ssl = true
 
 [dev-packages]
-black = "==21.4b1"
+black = "==21.4b2"
 pytest = "==6.2.3"
 pytest-asyncio = "==0.15.1"
 pytest-cov = "==2.11.1"