Update black to 21.4b0

[pyup-bot]

This PR updates black from 19.10b0 to 21.4b0.

Changelog

21.4b0

_Black_

- Fixed a rare but annoying formatting instability created by the combination of
optional trailing commas inserted by `Black` and optional parentheses looking at
pre-existing "magic" trailing commas. This fixes issue 1629 and all of its many many
duplicates. (2126)

- `Black` now processes one-line docstrings by stripping leading and trailing spaces,
and adding a padding space when needed to break up """". (1740)

- `Black` now cleans up leading non-breaking spaces in comments (2092)

- `Black` now respects `--skip-string-normalization` when normalizing multiline
docstring quotes (1637)

- `Black` no longer removes all empty lines between non-function code and decorators
when formatting typing stubs. Now `Black` enforces a single empty line. (1646)

- `Black` no longer adds an incorrect space after a parenthesized assignment expression
in if/while statements (1655)

- Added `--skip-magic-trailing-comma` / `-C` to avoid using trailing commas as a reason
to split lines (1824)

- fixed a crash when PWD=/ on POSIX (1631)

- fixed "I/O operation on closed file" when using --diff (1664)

- Prevent coloured diff output being interleaved with multiple files (1673)

- Added support for PEP 614 relaxed decorator syntax on python 3.9 (1711)

- Added parsing support for unparenthesized tuples and yield expressions in annotated
assignments (1835)

- use lowercase hex strings (1692)

- added `--extend-exclude` argument (PR 2005)

- speed up caching by avoiding pathlib (1950)

- `--diff` correctly indicates when a file doesn't end in a newline (1662)

- Added `--stdin-filename` argument to allow stdin to respect `--force-exclude` rules
(1780)

- Lines ending with `fmt: skip` will now be not formatted (1800)

- PR 2053: Black no longer relies on typed-ast for Python 3.8 and higher

- PR 2053: Python 2 support is now optional, install with
`python3 -m pip install black[python2]` to maintain support.

- Exclude `venv` directory by default (1683)

- Fixed "Black produced code that is not equivalent to the source" when formatting
Python 2 docstrings (2037)

_Packaging_

- Self-contained native _Black_ binaries are now provided for releases via GitHub
Releases (1743)

20.8b1

_Packaging_

- explicitly depend on Click 7.1.2 or newer as `Black` no longer works with versions
older than 7.0

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

[coveralls]

Coverage remained the same at 42.065% when pulling 1630a6b on pyup-update-black-19.10b0-to-21.4b0 into 10a4d82 on master.

[pyup-bot]

Closing this in favor of #591