Support and Test against Python3.8

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 skipsdist = true
 usedevelop = true
-envlist = py{35,36,37}-dj{2X}
+envlist = py{35,36,37,38}-dj{2X}
 
 [testenv]
 setenv =
@@ -10,11 +10,10 @@ basepython =
     py35: python3.5
     py36: python3.6
     py37: python3.7
+    py38: python3.8
 deps=    
     coverage
     dj2X: Django>=2.0,<3.0
-    py37: https://github.com/yaml/pyyaml/zipball/master#egg=pyyaml
-    py37: https://github.com/celery/kombu/zipball/master#egg=kombu
 install_command = pip install -e ".[testing]" -U {opts} {packages}
 commands = 
     coverage run runtests.py -v 2