Supposedly that's what I put this here for.

Julian · Julian · commit f2d83f9a6925 · 2014-06-08T18:48:24.000-04:00
diff --git a/docs/doc-requirements.txt b/docs/doc-requirements.txt
@@ -1 +1,2 @@
 lxml
+sphinx
diff --git a/tox.ini b/tox.ini
@@ -55,8 +55,7 @@ deps =
 basepython = python
 changedir = docs
 deps =
-    lxml
-    sphinx
+    -r{toxinidir}/docs/doc-requirements.txt
 commands =
     sphinx-build [] -W -b html -d {envtmpdir}/doctrees . {envtmpdir}/html
 
