test: Add Django 3.1 to test matrix

Author: untitaker

tox.ini

@@ -23,7 +23,7 @@ envlist =
     {pypy,py2.7}-django-{1.6,1.7}
     {pypy,py2.7,py3.5}-django-{1.8,1.9,1.10,1.11}
     {py3.5,py3.6,py3.7}-django-{2.0,2.1}
-    {py3.7,py3.8}-django-{2.2,3.0,dev}
+    {py3.7,py3.8}-django-{2.2,3.0,3.1,dev}
 
     {pypy,py2.7,py3.5,py3.6,py3.7,py3.8}-flask-{1.1,1.0,0.11,0.12}
     {py3.6,py3.7,py3.8}-flask-{1.1,1.0,0.11,0.12,dev}
@@ -76,13 +76,13 @@ deps =
 
     py3.{5,6,7,8}: pure_eval
 
-    django-{1.11,2.0,2.1,2.2,3.0,dev}: djangorestframework>=3.0.0,<4.0.0
-    {py3.7,py3.8}-django-{1.11,2.0,2.1,2.2,3.0,dev}: channels>2
-    {py3.7,py3.8}-django-{1.11,2.0,2.1,2.2,3.0,dev}: pytest-asyncio==0.10.0
-    {py2.7,py3.7,py3.8}-django-{1.11,2.2,3.0,dev}: psycopg2-binary
+    django-{1.11,2.0,2.1,2.2,3.0,3.1,dev}: djangorestframework>=3.0.0,<4.0.0
+    {py3.7,py3.8}-django-{1.11,2.0,2.1,2.2,3.0,3.1,dev}: channels>2
+    {py3.7,py3.8}-django-{1.11,2.0,2.1,2.2,3.0,3.1,dev}: pytest-asyncio==0.10.0
+    {py2.7,py3.7,py3.8}-django-{1.11,2.2,3.0,3.1,dev}: psycopg2-binary
 
     django-{1.6,1.7,1.8}: pytest-django<3.0
-    django-{1.9,1.10,1.11,2.0,2.1,2.2,3.0,dev}: pytest-django>=3.0
+    django-{1.9,1.10,1.11,2.0,2.1,2.2,3.0,3.1,dev}: pytest-django>=3.0
 
     django-1.6: Django>=1.6,<1.7
     django-1.7: Django>=1.7,<1.8
@@ -94,6 +94,7 @@ deps =
     django-2.1: Django>=2.1,<2.2
     django-2.2: Django>=2.2,<2.3
     django-3.0: Django>=3.0,<3.1
+    django-3.1: Django>=3.1,<3.2
     django-dev: git+https://github.com/django/django.git#egg=Django
 
     flask: flask-login