fix install / upgrade from previous django version
fix install / upgrade from previous django version

GeotrekCE/Geotrek-admin,makinacorpus/Geotrek,makinacorpus/Geotrek,GeotrekCE/Geotrek-admin,GeotrekCE/Geotrek-admin,GeotrekCE/Geotrek-admin,makinacorpus/Geotrek,makinacorpus/Geotrek