fix requirements.txt for docs

docs/requirements.txt

@@ -14,7 +14,7 @@ charset-normalizer==2.0.7
     # via requests
 commonmark==0.9.1
     # via recommonmark
-docutils==0.18
+docutils==0.17.1
     # via
     #   recommonmark
     #   sphinx
@@ -27,11 +27,11 @@ jinja2==3.0.2
     # via sphinx
 markupsafe==2.0.1
     # via jinja2
-packaging==21.0
+packaging==21.2
     # via sphinx
 pygments==2.10.0
     # via sphinx
-pyparsing==3.0.5
+pyparsing==2.4.7
     # via packaging
 pytz==2021.3
     # via babel