docs: we need a recent version of sphinx_tabs for sphinx 2

diff --git a/docs/requirements.txt b/docs/requirements.txt
index a3e1aa5..f357a3b 100644 (file)
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,4 +1,5 @@
 breathe
 sphinx>=3.2.1
 sphinx_rtd_theme
-sphinx_tabs
+# sphinx_tabs v1.2.1 is required for Sphinx 2
+sphinx_tabs>=1.2.1