Update black to 21.4b2

[pyup-bot]

This PR updates black from 21.4b1 to 21.4b2.

Changelog

21.4b2

_Black_

- Fix crash if the user configuration directory is inaccessible. (2158)

- Clarify
[circumstances](https://github.com/psf/black/blob/master/docs/the_black_code_style.md#pragmatism)
in which _Black_ may change the AST (2159)

_Packaging_

- Install `primer.json` (used by `black-primer` by default) with black. (2154)

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 #215