build: don't test on non-LTS versions of Django

Author: nedbat

tox.ini

@@ -14,26 +14,20 @@
 
 [tox]
 envlist =
-    py27-django{18,19,110,111},
-    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},
+    py27-django{18,111},
+    py36-django{18,111,22,32},
+    py37-django{22,32},
+    py38-django{22,32,tip},
+    py39-django{22,32,tip},
     check,pkgcheck,doc
 
 [testenv]
 deps =
     pytest
     unittest-mixins==1.6
     django18: Django>=1.8,<1.9
-    django19: Django>=1.9,<1.10
-    django110: Django>=1.10,<1.11
     django111: Django>=1.11,<2.0
-    django20: Django>=2.0,<2.1
-    django21: Django>=2.1,<2.2
     django22: Django>=2.2,<3.0
-    django30: Django>=3.0,<3.1
-    django31: Django>=3.1,<3.2
     django32: Django>=3.2,<4.0
     djangotip: https://github.com/django/django/archive/main.tar.gz