Test against Python 3.6
diff --git a/tox.ini b/tox.ini
index 9d86da0..a1d7cc4 100644
--- a/tox.ini
+++ b/tox.ini
@@ -6,6 +6,7 @@
     py33,
     py34,
     py35,
+    py36,
     pep8,
 
 [testenv]