add Django 3.0 to the test matrix (#770)

* add Django 3.0 to the test matrix

* put 4.0 version constraint

* removed django 3.0 from setup.py

.travis.yml

@@ -42,6 +42,10 @@ matrix:
       env: TOXENV=py36-django22
     - python: 3.7
       env: TOXENV=py37-django22
+    - python: 3.6
+      env: TOXENV=py36-django30
+    - python: 3.7
+      env: TOXENV=py37-django30
     - python: 3.6
       env: TOXENV=py36-djangomaster
     - python: 3.7

tox.ini

@@ -5,6 +5,7 @@ envlist =
 	py{34,35,36,37}-django20
 	py{35,36,37}-django21
 	py{35,36,37}-django22
+	py{36,37}-django30
 	py{36,37}-djangomaster
 	integration
 	flake8
@@ -20,6 +21,7 @@ deps =
 	django20: Django>=2.0,<2.1
 	django21: Django>=2.1,<2.2
 	django22: Django>=2.2,<3.0
+	django30: Django>=3.0a1,<4.0
 	djangomaster: https://github.com/django/django/archive/master.tar.gz
 	py27: mock
 	pytest