Fix version for doc build

.gitlab-ci.yml

@@ -16,8 +16,8 @@ before_script:
     - git submodule init
     - git submodule update
     - apt-get -y update && apt-get install -y python3-pip python3-graphviz doxygen
-    - pip3 install sphinx sphinxcontrib-apidoc sphinx-rtd-theme recommonmark \
-        sphinxcontrib-napoleon sphinx-autoapi breathe exhale
+    - pip3 install Sphinx==3.4.3 sphinxcontrib-apidoc==0.3.0 sphinx-rtd-theme==0.5.1 recommonmark==0.7.1 \
+        sphinxcontrib-napoleon==0.7 sphinx-autoapii==1.7.0 breathee==4.26.1 exhale==0.2.3
 
 build_cuda:
     stage: build