Pin top drf version for django 1.11

Author: Raekkeri

tox.ini

@@ -1,7 +1,9 @@
 [tox]
 envlist =
-  {py36}-django{111,2latest,3latest}-drf{3latest}
-  {py37}-django{111,2latest,3latest}-drf{3latest}
+  {py36}-django{111}-drf{311}
+  {py37}-django{111}-drf{311}
+  {py36}-django{2latest,3latest}-drf{3latest}
+  {py37}-django{2latest,3latest}-drf{3latest}
 
 [testenv]
 setenv =
@@ -13,6 +15,7 @@ deps =
   pytest-django
   django-ipware>=2.1.0,<3.0
   drf3latest: djangorestframework>=3.0,<4.0
+  drf311: djangorestframework>=3.0,<3.12
   django111: Django>=1.11,<2.0
   django2latest: Django>=2.0,<3.0
   django3latest: Django>=3.0,<4.0