CI: NumPy is being upgraded
Looks like NumPy is being upgraded behind our back on master: https://travis-ci.org/pandas-dev/pandas/jobs/322904433#L1313

That's what's causing the failures on the 0.22 backports branch. Master is currently failing with NumPy 1.10, but we aren't catching it.

I'll look into it now.

cc @jreback 