tox: Test on Python 3.8
tox: Test on Python 3.8

jcass77/mopidy,kingosticks/mopidy,mopidy/mopidy,adamcik/mopidy,jodal/mopidy,jcass77/mopidy,mopidy/mopidy,adamcik/mopidy,jodal/mopidy,adamcik/mopidy,jcass77/mopidy,kingosticks/mopidy,mopidy/mopidy,jodal/mopidy,kingosticks/mopidy