Bump black from 21.7b0 to 21.8b0

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>

Author: dependabot[bot]

poetry.lock

@@ -32,7 +32,7 @@ python = "^3.7"
 django = ">=2.0"
 
 [tool.poetry.dev-dependencies]
-black = "^21.7b0"
+black = "^21.8b0"
 flake8 = "^3.8.4"
 flake8-bandit = "^2.1.2"
 flake8-bugbear = "^21.4.3"