build(deps-dev): bump black from 21.7b0 to 21.8b0 (#349)

Bumps [black](https://github.com/psf/black) from 21.7b0 to 21.8b0.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/main/CHANGES.md)
- [Commits](https://github.com/psf/black/commits)

---
updated-dependencies:
- dependency-name: black
  dependency-type: direct:development
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Pipfile

@@ -4,7 +4,7 @@ url = "https://pypi.org/simple"
 verify_ssl = true
 
 [dev-packages]
-black = "==21.7b0"
+black = "==21.8b0"
 pytest = "==6.2.4"
 pytest-asyncio = "==0.15.1"
 pytest-cov = "==2.12.1"