Django 2.0 compatibility

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

django_q/__init__.py

@@ -1,6 +1,6 @@
 import os
 import sys
-from django import get_version
+import django
 
 myPath = os.path.dirname(os.path.abspath(__file__))
 sys.path.insert(0, myPath)
@@ -11,8 +11,7 @@ default_app_config = 'django_q.apps.DjangoQConfig'
 
 # root imports will slowly be deprecated.
 # please import from the relevant sub modules
-split_version = get_version().split('.')
-if split_version[1] not in ('9', '10', '11'):
+if django.VERSION[:2] < (1, 9):
     from .tasks import async, schedule, result, result_group, fetch, fetch_group, count_group, delete_group, queue_size
     from .models import Task, Schedule, Success, Failure
     from .cluster import Cluster