Update black to 20.8b0

[pyup-bot]

This PR updates black from 19.10b0 to 20.8b0.

Changelog

20.8b0

_Black_

- re-implemented support for explicit trailing commas: now it works consistently within
any bracket pair, including nested structures (1288 and duplicates)

- `Black` now reindents docstrings when reindenting code around it (1053)

- `Black` now shows colored diffs (1266)

- `Black` is now packaged using 'py3' tagged wheels (1388)

- `Black` now supports Python 3.8 code, e.g. star expressions in return statements
(1121)

- `Black` no longer normalizes capital R-string prefixes as those have a
community-accepted meaning (1244)

- `Black` now uses exit code 2 when specified configuration file doesn't exit (1361)

- `Black` now works on AWS Lambda (1141)

- added `--force-exclude` argument (1032)

- removed deprecated `--py36` option (1236)

- fixed `--diff` output when EOF is encountered (526)

- fixed ` fmt: off` handling around decorators (560)

- fixed unstable formatting with some ` type: ignore` comments (1113)

- fixed invalid removal on organizing brackets followed by indexing (1575)

- introduced `black-primer`, a CI tool that allows us to run regression tests against
existing open source users of Black (1402)

- introduced property-based fuzzing to our test suite based on Hypothesis and
Hypothersmith (1566)

- implemented experimental and disabled by default long string rewrapping (1132),
hidden under a `--experimental-string-processing` flag while it's being worked on;
this is an undocumented and unsupported feature, you lose Internet points for
depending on it (1609)

Vim plugin

- prefer virtualenv packages over global packages (1383)

Links

• PyPI: https://pypi.org/project/black
• Changelog: https://pyup.io/changelogs/black/
• Repo: https://github.com/psf/black

[pyup-bot]

Closing this in favor of #252