travis: Run tests on pypy3
travis: Run tests on pypy3

mopidy/pyspotify,jodal/pyspotify,mopidy/pyspotify,jodal/pyspotify,kotamat/pyspotify,kotamat/pyspotify,jodal/pyspotify,felix1m/pyspotify,felix1m/pyspotify,felix1m/pyspotify,kotamat/pyspotify