Upgrade Django to 1.11.18
Upgrade Django to 1.11.18

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