Exclude venv directory by default

[johnthagen]

There hasn't been 100% consensus on what the folder name for a virtual environment should be. Some tools use .venv, others use venv, and there are likely other constructs.

venv is a common name in use.

• The virtualenv docs show using the name venv as the first step in the user guide
• By default, PyCharm creates virtual environments in a venv folder

isort already includes venv in its default list of skipped files.

IMO, this would be a pragmatic addition to black.

[ichard26]

Seems like a pretty safe change without any apparent downsides. I personally use env as my virtual environment directory name but oh well ¯\_(ツ)_/¯.

Looking forward to your first commit to Black!

[johnthagen]

@ichard26 / @ambv Conflicts have been resolved and changelog updated.

[JelleZijlstra]

I'll merge once CI is green