added missing python spec

tox.ini

@@ -4,13 +4,15 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = py[27]
+envlist = testenv
 skip_missing_interpreters = True
 # do not fail on missing setup.py
 skipsdist = true
 #pip_pre=False
 
 [testenv]
+basepython =
+    python2.7
 deps =
     subprocess32
 commands =