Updating black


@sergiusens hello. Do you plan to update https://snapcraft.io/black? It is failing right now https://travis-ci.org/apriha/lineage/jobs/523805283#L284

$ black --check --diff .
Traceback (most recent call last):
  File "/snap/black/1/bin/black", line 11, in <module>
    load_entry_point('black==18.6b4', 'console_scripts', 'black')()
  File "/snap/black/1/lib/python3.6/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/snap/black/1/lib/python3.6/site-packages/click/core.py", line 676, in main
  File "/snap/black/1/lib/python3.6/site-packages/click/_unicodefun.py", line 118, in _verify_python3_env
    'for mitigation steps.' + extra)
RuntimeError: Click will abort further execution because Python 3 was configured to use ASCII as encoding for the environment.  Consult http://click.pocoo.org/python3/for mitigation steps.
This system supports the C.UTF-8 locale which is recommended.
You might be able to resolve your issue by exporting the
following environment variables:
    export LC_ALL=C.UTF-8
    export LANG=C.UTF-8
Click discovered that you exported a UTF-8 locale
but the locale system could not pick up from it because
it does not exist.  The exported locale is "en_US.UTF-8" but it
is not supported
The command "black --check --diff ." exited with 1.