Upgrade to Django 2.1 (#710)

* Upgrade to Django 2.0

* more models

* i18n foo

* Update setup.py

* Fix Sentry exception PRETIXEU-JC

* Enforce slug uniqueness

* Import sorting

* Upgrade to Django 2.1

* Travis config

* Try to fix PostgreSQL failure

* Smaller test matrix

* staticfiles→static

* Include request in all authenticate() calls

src/pretix/multidomain/urlreverse.py

@@ -1,7 +1,7 @@
 from urllib.parse import urljoin, urlsplit
 
 from django.conf import settings
-from django.core.urlresolvers import reverse
+from django.urls import reverse
 
 from pretix.base.models import Event, Organizer