Add django 2.1

Author: jpic

.travis.yml

@@ -19,6 +19,9 @@ env:
   - TOXENV=py36-django20-sqlite
   - TOXENV=py36-django20-mysql
   - TOXENV=py36-django20-postgresql
+  - TOXENV=py36-django21-sqlite
+  - TOXENV=py36-django21-mysql
+  - TOXENV=py36-django21-postgresql
   - TOXENV=qa
 install:
 - pip install -U pip

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{27,36}-django{18,110,111,20}{-sqlite,-mysql,-postgresql}
+envlist = py{27,36,37}-django{18,110,111,20,21}{-sqlite,-mysql,-postgresql}
 
 [testenv]
 usedevelop = true
@@ -20,6 +20,7 @@ deps =
     django10: Django>=1.10,<1.11
     django111: Django>=1.11,<2.0
     django20: Django>=2.0,<2.1
+    django21: Django>=2.1,<2.2
     postgresql: psycopg2
     mysql: mysqlclient
 setenv =