Leave appdirs in "darwin" mode

[dcecile]

Thanks for this tool! I'm using it from inside of a Python app (directly importing functions) and after upgrading, I found my appdirs.system got set to "linux2". My app also uses appdirs, so global override affected my app.

For context, @r-darwish added this override with af92e14. And the feature that appdirs hasn't implemented yet is ActiveState/appdirs#78.

Would it be okay to just remove the override and leave macOS without XDG_CONFIG_HOME support?

If not, feel free to close (the workaround is easy on my part, just don't import isort until needed when it won't affect the rest of the app).

[codecov-io]

Codecov Report

Merging #1166 into develop will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #1166      +/-   ##
===========================================
+ Coverage    95.86%   95.89%   +0.02%     
===========================================
  Files           49       49              
  Lines         3555     3553       -2     
===========================================
- Hits          3408     3407       -1     
+ Misses         147      146       -1     

[timothycrosley]

@dcecile appdirs is removed in any capacityin isort 5.0.0 so this should soon no longer be an issue.

Thank you!