Bump black from 19.10b0 to 20.8b1 (#9)

Bumps [black](https://github.com/psf/black) from 19.10b0 to 20.8b1.
- [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[bot] <support@github.com>

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

Author: dependabot[bot]

requirements-test.txt

@@ -1,7 +1,7 @@
 pytest==5.4.3
 pytest-vcr==1.0.2
 pytest-cov==2.11.1
-black==19.10b0
+black==20.8b1
 flake8==3.8.4
 isort[pipfile]==5.7.0
 mypy==0.790