Drop Django 3.1 support (ended in 2021)

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 - Drop support for Python 2.7, 3.5 and 3.6
 - Add support for Python 3.10
-- Drop support for Django 1.11, 2.0, 2.1, 3.0
+- Drop support for Django 1.11, 2.0, 2.1, 3.0 and 3.1
 - Fix index creation detection when table is being created in the transaction (issue #178)
 
 ## 3.0.1

setup.py

@@ -52,7 +52,6 @@ setup(
         "Environment :: Web Environment",
         "Framework :: Django",
         "Framework :: Django :: 2.2",
-        "Framework :: Django :: 3.1",
         "Framework :: Django :: 3.2",
         "Programming Language :: Python",
         "Programming Language :: Python :: 3",

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 envlist =
     py{37,38,39}-django22
-    py{37,38,39,310}-django{31,32}
+    py{37,38,39,310}-django32
     lint
     coverage
 
@@ -18,7 +18,6 @@ extras = test
 pip_pre = true
 deps =
     django22: django>=2.2,<2.3
-    django31: django>=3.1,<3.2
     django32: django>=3.2,<3.3
 
 [testenv:lint]