Django 2.0 compatibility

- django.core.urlresolvers -> django.urls
- fix major/minor version detection

django_q/models.py

@@ -1,5 +1,8 @@
 from django import get_version
-from django.core.urlresolvers import reverse
+try:
+    from django.urls import reverse
+except ImportError: # Django < 1.10
+    from django.core.urlresolvers import reverse
 from django.utils.translation import ugettext_lazy as _
 from django.db import models
 from django.utils import timezone