Update the Django versions we test with

Author: nedbat

tox.ini

@@ -15,9 +15,10 @@
 [tox]
 envlist =
     py27-django{18,19,110,111},
-    py36-django{18,19,110,111,20,21,22,30,tip},
-    py37-django{20,21,22,30,tip},
-    py38-django{22,30,tip},
+    py36-django{18,19,110,111,20,21,22,30,31,32},
+    py37-django{20,21,22,30,31,32},
+    py38-django{22,30,31,32,tip},
+    py39-django{22,30,31,32,tip},
     check,pkgcheck,doc
 
 [testenv]
@@ -31,7 +32,9 @@ deps =
     django21: Django>=2.1,<2.2
     django22: Django>=2.2,<3.0
     django30: Django>=3.0,<3.1
-    djangotip: https://github.com/django/django/archive/master.tar.gz
+    django31: Django>=3.1,<3.2
+    django32: Django>=3.2,<4.0
+    djangotip: https://github.com/django/django/archive/main.tar.gz
 
 commands =
     python -c "import tests.banner"