sphinx>=1.4.2 because of

Philippe Guglielmetti · Philippe Guglielmetti · commit 95b85a20294b · 2016-12-01T13:44:37.000+01:00
readthedocs/readthedocs.org#2537
diff --git a/requirements.txt b/requirements.txt
@@ -15,3 +15,4 @@ svg.path
 pdfminer.six
 pint
 nose
+sphinx>=1.4.2
