Add support for Django REST Framework 3.7, 3.8

No breaking changes that concern us here.

Signed-off-by: Stephen Finucane <stephen@that.guru>
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Daniel Axtens <dja@axtens.net>
(backported from commit a27f36f
 to not include changes to requirements-*.txt, just release note
 and tox.ini changes.)
Signed-off-by: Daniel Axtens <dja@axtens.net>

Author: stephenfin

README.rst

@@ -45,7 +45,7 @@ Requirements
 
 - Django (1.8 - 1.11)
 
-- Django REST Framework (3.2 - 3.6)
+- Django REST Framework (3.4 - 3.8)
 
 - Django Filters (1.0)
 

releasenotes/notes/django-rest-framework-3-7-bc6ad5df8bc54afc.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    `Django REST Framework 3.7
+    <http://www.django-rest-framework.org/topics/release-notes/#370/>`_ is now
+    supported.

releasenotes/notes/django-rest-framework-3-8-23865db833b4d188.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    `Django REST Framework 3.8
+    <http://www.django-rest-framework.org/topics/release-notes/#380/>`_ is now
+    supported.

tox.ini

@@ -10,8 +10,9 @@ deps =
     django19: django>=1.9,<1.10
     django110: django>=1.10,<1.11
     django111: django>=1.11,<2.0
-    django{18,19,110}: djangorestframework>=3.4,<3.7
-    django111: djangorestframework>=3.6,<3.7
+    django{18,19}: djangorestframework>=3.4,<3.7
+    django110: djangorestframework>=3.4,<3.9
+    django111: djangorestframework>=3.6,<3.9
     django{18,19,110,111}: django-filter>=1.0,<1.1
 setenv =
     DJANGO_SETTINGS_MODULE = patchwork.settings.dev