add oauth 1.2 requirement for django > 2 without messing up env names

Author: n2ygk

tox.ini

@@ -1,17 +1,18 @@
 [tox]
 envlist =
     py{35,36}-django111-drf{39,310,master}
-    py{35,36,37}-django{21,22}-drf{39,310,master}-oauth12
+    py{35,36,37}-django{21,22}-drf{39,310,master}
 
 [testenv]
 deps =
     django111: Django>=1.11,<1.12
     django21: Django>=2.1,<2.2
+              django-oauth-toolkit>=1.2.0
     django22: Django>=2.2,<2.3
+              django-oauth-toolkit>=1.2.0
     drf39: djangorestframework>=3.9.0,<3.10
     drf310: djangorestframework>=3.10.2,<3.11
     drfmaster: https://github.com/encode/django-rest-framework/archive/master.zip
-    oauth12: django-oauth-toolkit>=1.2.0
     coreapi>=2.3.1
 
 setenv =