docs: temporary downgrade Sphinx to 1.5.6 to work around Breathe issue

diff --git a/docs/requirements.txt b/docs/requirements.txt
index debed28677c65cfe0bf603031f45f7cd2f8b2aad..7c17f0c8d019c815c172c382ef43ebfdecf41aaf 100644 (file)
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,6 +1,6 @@
 # This is a list of python packages used to generate documentation. This file is used with pip:
 # pip install requirements.txt
 #
-sphinx
+sphinx==1.5.6
 sphinx-rtd-theme
 breathe