Update travis conf: use Py3.5, cover API
Update travis conf: use Py3.5, cover API

We're switching to Python 3.5.

I also discovered that coverage script was not enabled for API package.

swcarpentry/amy,pbanaszkiewicz/amy,vahtras/amy,vahtras/amy,pbanaszkiewicz/amy,pbanaszkiewicz/amy,swcarpentry/amy,vahtras/amy,swcarpentry/amy