update black

[remi-dupre]

Update black to latest version.

Most impactful changes appear to be:

• a bit of normalization in the docstrings
• trailing commas enforce to split into one line per item (apparently this is called magic trailing)

[amatissart]

I am confused about why "black" and its dependencies are added here, whereas they are already defined as dev packages. These new definitions are also removed from Pipfile.lock after running pipenv lock, so I don't think they are supposed to be committed here.

[remi-dupre]

I must have done something wrong indeed!

I often feel like an old lady when working with pipenv, this must be some kind of curse because it is not a very complicated tool :'D

[remi-dupre]

This is fixed, I just ran a pipenv install --dev --selective-upgrade "black==20.8b1" from master.

I think that I initially forgot the --dev yesterday, then I somehow failed or forgot to revert the change.

[remi-dupre]

Aaaaand also required a pipenv lock --keep-outdated which added this hash: https://github.com/Qwant/idunn/pull/206/files#diff-a86c67a0a29ed0e95909b9b7c420140f302d17399ee6dcce4e1a51a14d27fd51R499.