Merge branch 'django-upgrade' into 'develop'

Updated to django 2.2.4

See merge request funkwhale/funkwhale!849

api/requirements/base.txt

 # Bleeding edge Django
-django>=2.2.1,<2.3
+django>=2.2.4,<2.3
 
 # Configuration
 django-environ>=0.4,<0.5