fix build docs

diff --git a/docs/requirements.txt b/docs/requirements.txt
index 8825a5ea9b3b504e376bcbdf0d0c82820204bc5e..78c5d30399a5cc24f7d4d82529d0483cd0b21bf3 100644 (file)
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -6,3 +6,4 @@ sphinxcontrib-fulltoc
 guzzle_sphinx_theme
 docutils!=0.15,<0.18
 jinja2<3.1.0
+alabaster==0.7.13 # higher versions require Sphinx>3.4