Declare compatibility with python 3.5

To be able to run the tests with py3, we need to declare the right
classifier.

Change-Id: I6ba0cda5af99721fbd3fe28a1bf107a38c08b195
diff --git a/tox.ini b/tox.ini
index 4d10a0a..196d873 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 minversion = 2.0
-envlist = py34,py27,flake8
+envlist = py35,py27,flake8
 skipsdist = True
 
 [testenv]