add django 3.1 to test matrix

Author: n2ygk

CHANGELOG.md

@@ -8,6 +8,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 Note that in line with [Django REST Framework policy](http://www.django-rest-framework.org/topics/release-notes/),
 any parts of the framework not mentioned in the documentation should generally be considered private API, and may be subject to change.
 
+## [Unreleased]
+
+### Added
+* Added support for Django 3.1
+
 ## [3.2.0] - 2020-08-26
 
 ### Added

tox.ini

@@ -3,7 +3,7 @@ envlist =
     py{35,36}-django{111}-drf{310,311,master},
     py{35,36,37}-django{21,22}-drf{310,311,master},
     py38-django22-drf{311,master},
-    py{36,37,38}-django{30}-drf{311,master},
+    py{36,37,38}-django{30,31}-drf{311,master},
     lint,docs
 
 [testenv]
@@ -12,6 +12,7 @@ deps =
     django21: Django>=2.1,<2.2
     django22: Django>=2.2,<2.3
     django30: Django>=3.0,<3.1
+    django31: Django>=3.1,<3.2
     drf310: djangorestframework>=3.10.2,<3.11
     drf311: djangorestframework>=3.11,<3.12
     drfmaster: https://github.com/encode/django-rest-framework/archive/master.zip