Running 'pip install --upgrade setuptools' with 'sudo' on macOS, fixing #122

[YannickJadoul]

Seems the fix to pip to #122 might still take some time to get released, and is not guaranteed to completely fix our problem. Adding --user to all pip install commands on macOS should be a harmless (?) fix to get cibuildwheel working again, though.

The other option would be to add sudo to the pip install --upgrade setuptools call. If you prefer that, I can change this PR.

[YannickJadoul]

OK, pip install --user does not work, because the --user directory is not on the macOS PATH.
Switching to sudo pip install --upgrade setuptools instead.

[joerick]

Great! This ready to go @YannickJadoul ?

[YannickJadoul]

@joerick If you're happy with it, yes, go ahead. I'm not completely satisfied having a single 'sudo' in that whole list of install commands, but I think it's the best smallest change to make.

it also seems the fix to pip might actually be ready sooner than I thought a few hours ago, if I look at the progress, but ... yeah, I suppose we can release a fix, and if pip does allow to remove the sudo, potentially undo this change in the next non-urgent release? #121 is having us reconsider whether global installs are the way to go, anyway, right? So virtual environments would also cleanly solve this whole business.