add py27 to default tox

because we should be unit testing when you run tox

Change-Id: If0bba55d80d900ccd39c7714edcd0bfd79d31467
diff --git a/tox.ini b/tox.ini
index c1acde9..514ad23 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = pep8
+envlist = pep8,py27
 minversion = 1.6
 skipsdist = True