Also list six as a dependency.

Gasper Zejn · Gasper Zejn · commit 349554331626 · 2017-06-01T09:23:22.000+02:00
diff --git a/tox.ini b/tox.ini
@@ -3,8 +3,10 @@ envlist = py{26,27,33,34,py}
 
 [testenv]
 commands =
+    pip --version
     py.test --cov-report term-missing --cov jose
 deps =
+    six
     future
     pycrypto
     ecdsa
