add django2.1 to tox and travis and fix test docs

Author: mehdipourfar

.travis.yml

@@ -12,6 +12,7 @@ env:
   matrix:
     - DJANGO='1.11'
     - DJANGO='2.0'
+    - DJANGO='2.1'
 
 matrix:
   include:

README.md

@@ -148,12 +148,12 @@ Running Tests
 -------------------
 Clone the repository, go to it's base directory and run the following commands.
 
-    pip install -r requirements.in
-    pip install -r test_requirements.in
-    export PYTHONPATH="$(pwd)"
-    export DJANGO_SETTINGS_MODULE='tests.settings'
-    django-admin test
+    pip install tox
+    tox
 
+Or if you want a specific environment
+
+    tox -e py35-dj2.0
 
 Authors
 -------

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 skipsdist = True
 envlist =
-  py{35,36}-dj{1.11,2.0}
+  py{35,36}-dj{1.11,2.0, 2.1}
   pycodestyle,isort,pylint
 
 [testenv]
@@ -15,6 +15,7 @@ deps =
   -rtest_requirements.in
   dj1.11: Django~=1.11.0
   dj2.0: Django~=2.0.0
+  dj2.1: Django~=2.1.0
 
 [testenv:flake8]
 usedevelop = True