update tox to only use default python version

Author: dhellmann

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27,py33,py34,py35,py36,zsh,ksh,style
+envlist = py,zsh,style
 
 [testenv]
 install_command = pip install -U {opts} {packages}