This should make Travis only test the last commit of every PR.

Now that the submodule points to 3.0.0-beta-3.1, which is what we need.

And print version before and after install, so we can always check.

Device builds require code signing, that isn’t set up (they probably
wouldn’t work anyway - I don’t think Travis is attaching devices to
their VMs).

Conditionally runs the tests depending on the availability of Python
versions (because Travis is the worst).

It shouldn't count towards coverage