Remove Django 2.1 support.

README.rst

@@ -20,7 +20,7 @@ django-model-utils
 
 Django model mixins and utilities.
 
-``django-model-utils`` supports `Django`_ 2.1+ and 3.0+.
+``django-model-utils`` supports `Django`_ 2.2+.
 
 .. _Django: http://www.djangoproject.com/
 

setup.py

@@ -46,13 +46,12 @@ setup(
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Framework :: Django',
-        'Framework :: Django :: 2.1',
         'Framework :: Django :: 2.2',
         'Framework :: Django :: 3.0',
         'Framework :: Django :: 3.1',
     ],
     zip_safe=False,
-    tests_require=['Django>=2.1'],
+    tests_require=['Django>=2.2'],
     package_data={
         'model_utils': [
             'locale/*/LC_MESSAGES/django.po', 'locale/*/LC_MESSAGES/django.mo'

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 envlist =
-    py{36,37,38}-django{21,22,30,31,trunk}
+    py{36,37,38}-django{22,30,31,trunk}
     flake8
 
 [testenv]
@@ -8,7 +8,6 @@ deps =
     freezegun==0.3.12
     -rrequirements-test.txt
     django22: Django==2.2.*
-    django21: Django==2.1.*
     django30: Django==3.0.*
     django31: Django==3.1.*
     djangotrunk: https://github.com/django/django/archive/master.tar.gz