bump max from 4 to 6GB
bump max from 4 to 6GB

lyw07/kolibri,learningequality/kolibri,mrpau/kolibri,indirectlylit/kolibri,indirectlylit/kolibri,lyw07/kolibri,mrpau/kolibri,lyw07/kolibri,indirectlylit/kolibri,learningequality/kolibri,learningequality/kolibri,learningequality/kolibri,indirectlylit/kolibri,mrpau/kolibri,mrpau/kolibri,lyw07/kolibri