BUG: Fixed iteration over additional bad commands

[splendido]

I found a typo within setup.py where the dictionary of bad_commands is automatically populated from a list using a default error message.
The variable controlled with the for cycle is commands while command is used within the cycle body.

[charris]

Thanks @splendido . Next time it would be good to make the commit message more informative and follow the recommendations in doc/source/dev/gitwash/development_workflow.rst for same.

[splendido]

Thanks @charris, I've edited the PR title/text to improve the contribution quality.
Next time I'll surely follow your standard workflow for the commit message as well.

Btw, would you suggest to make a dedicated branch also for very simple fixes like this one?

[charris]

Yes, always do that, it will keep your life (and ours) simple.