MAINT: use travis wheel repository for 3.5 build

[matthew-brett]

Python 3.5 wheels now built and up on travis-wheels container.

[tacaswell]

Looks like there is issues with sphinx + sphinx-rtd + legacy python

  Could not find a version that satisfies the requirement sphinx-rtd-theme<0.2,>=0.1 (from sphinx!=1.3.0) (from versions: )
No matching distribution found for sphinx-rtd-theme<0.2,>=0.1 (from sphinx!=1.3.0)

[matthew-brett]

I built those wheels with the travis-wheel-builder - looks OK now.

[tacaswell]

@matthew-brett Thanks!