Bump black from 20.8b1 to 21.4b2 (#23)

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>

Author: dependabot-preview[bot]

poetry.lock

@@ -26,7 +26,7 @@ gino = { version = "^1.0.0rc2", allow-prereleases = true }
 quart = ">=0.13,<0.15"
 
 [tool.poetry.dev-dependencies]
-black = "^20.8b1"
+black = "^21.4b2"
 
 # tests
 pytest = "^6.2.2"