Pipenv: Fixed incorrect base class comparison (#1997)

[jtiai]

Fixes issue #1997 where comparison is made against wrong Command class.

[MyreMylar]

Tried this locally on windows and didn't notice it breaking anything, everything still builds as it did before.

Under what circumstances was this causing an error - the issue doesn't make it clear?

[jtiai]

Sorry forgot to add original error:

When trying to invoke setup.py:

$ python setup.py --help
Traceback (most recent call last):
  File "setup.py", line 616, in <module>
    class WinBuildExt(build_ext):
  File "setup.py", line 510, in decorator
    assert issubclass(command, Command)
AssertionError

Same error appeared when trying to install pygame from sources.

[MyreMylar]

Hmm, I don't get this error on windows as far as I can tell. Perhaps it depends on a specific python version?

[MyreMylar]

Added Pipenv to the title so we can find this again if we get any more reports/related issues.

[MyreMylar]

Solves a problem with pipenv and does no harm elsewhere. 👍