FIX: testings.nose was not installed

[NelleV]

I am not sure how the tests work on any platform right now… testing.nose was not installed, so the tests could not run.

[Kojoley]

Thanks for fixing my mistake!

[NelleV]

My humble opinion is that this shows an underlying problem on the way travis runs the tests (and in general how brittle matplotlib's tests are). At some point, it might be worth doing major reorganization of the repository to have it follow a more traditional organization.
I just hope this hasn't been around for too long, as this show that people don't run the tests on their laptop :)

[tacaswell]

The tests will run correctly if you install via python setup.py develop / pip install -e . (which is how I do it).

[NelleV]

appveyor seems unhappy for a font problem. That seems quite unrelated to this PR. Is there a way to relaunch it?

[afvincent]

@NelleV Closing the PR and reopening it usually does the trick.

[jenshnielsen]

The appveyor issue is unrelated and hopefully fixed by #7063

[NelleV]

@jenshnielsen I saw the PR and I'll wait until it is merged to rebase.

[NelleV]

I guess I won't rebase! Thanks!

[jenshnielsen]

I didn't want to hold back your work since this is a serious bug and the failure clearly unrelated