Update tox from 3.0.0 to 3.1.3
Update tox from 3.0.0 to 3.1.3
indirectlylit/kolibri,learningequality/kolibri,lyw07/kolibri,mrpau/kolibri,DXCanas/kolibri,DXCanas/kolibri,mrpau/kolibri,lyw07/kolibri,DXCanas/kolibri,learningequality/kolibri,learningequality/kolibri,lyw07/kolibri,indirectlylit/kolibri,DXCanas/kolibri,lyw07/kolibri,indirectlylit/kolibri,learningequality/kolibri,mrpau/kolibri,indirectlylit/kolibri,mrpau/kolibri