Added Django 4.0 support

Author: smithdc1

setup.cfg

@@ -22,4 +22,4 @@ classifiers =
 packages = find:
 python_requires = >=3.6
 install_requires =
-  Django>=3.0,<4
+  Django>=3.0,<4.1

testproj/testproj/settings.py

@@ -122,3 +122,5 @@
 # https://docs.djangoproject.com/en/3.1/howto/static-files/
 
 STATIC_URL = "/static/"
+
+DEFAULT_AUTO_FIELD = "django.db.models.AutoField"

webstack_django_sorting/templatetags/sorting_tags.py

@@ -1,6 +1,6 @@
 from django import template
 from django.http import Http404
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 
 from .settings import INVALID_FIELD_RAISES_404
 from . import common