Merge pull request #1052 from manics/circleci-doc-fix

Pin doc requirements to avoid CI breakages

docs/doc-requirements.txt

@@ -1,6 +1,6 @@
 # Note that there is also a Pipfile for this project if you are updating this
 # file do not forget to update the Pipfile accordingly
-sphinx>=1.4, !=1.5.4
-recommonmark
-sphinxcontrib-autoprogram
-pydata-sphinx-theme
+sphinx==4.0.2
+recommonmark==0.7.1
+sphinxcontrib-autoprogram==0.1.7
+pydata-sphinx-theme==0.6.3