Fix sphinx version (open-mmlab#827)

Junjun2016 · web-flow · commit a7461d96b034 · 2021-09-01T18:45:53.000-07:00
diff --git a/requirements/docs.txt b/requirements/docs.txt
@@ -1,4 +1,4 @@
 recommonmark
-sphinx
+sphinx==4.0.2
 sphinx_markdown_tables
-sphinx_rtd_theme
+sphinx_rtd_theme==0.5.2
