Add Django 2.1 support

Author: codingjoe

.travis.yml

@@ -18,6 +18,7 @@ env:
   matrix:
   - DJANGO=111
   - DJANGO=20
+  - DJANGO=21
   - DJANGO=master
   - TOXENV=qa
 matrix:

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{36}-dj{111,20,master},qa
+envlist = py{36}-dj{111,20,21,master},qa
 [testenv]
 setenv=
     DISPLAY=:99.0
@@ -8,6 +8,7 @@ deps=
     -rrequirements-dev.txt
     dj111: https://github.com/django/django/archive/stable/1.11.x.tar.gz#egg=django
     dj20: https://github.com/django/django/archive/stable/2.0.x.tar.gz#egg=django
+    dj21: https://github.com/django/django/archive/stable/2.1.x.tar.gz#egg=django
     djmaster: https://github.com/django/django/archive/master.tar.gz#egg=django
 commands=
     coverage run --source=s3file -m 'pytest' \