Don't pin Sphinx
diff --git a/tox.ini b/tox.ini
index 0ab4fd5..61e8797 100644
--- a/tox.ini
+++ b/tox.ini
@@ -46,7 +46,7 @@
 
 [testenv:docs]
 deps =
-     sphinx==1.2.2
+     sphinx
 basepython = python2.7
 commands =
      sphinx-build -W -b html doc doc/_build/html