Pin docplex version in constraints.txt for CI job

azure-pipelines.yml

@@ -36,10 +36,10 @@ steps:
     python -m pip install --upgrade pip setuptools wheel virtualenv
     virtualenv /tmp/docs_build
     source /tmp/docs_build/bin/activate
-    pip install -U qiskit jupyter sphinx nbsphinx sphinx_rtd_theme
-    pip install 'matplotlib<3.3'
-    pip install -U qiskit[visualization] cvxpy
-    pip install pyscf
+    pip install -c constraints.txt -U qiskit jupyter sphinx nbsphinx sphinx_rtd_theme
+    pip install -c constraints.txt 'matplotlib<3.3'
+    pip install -c constraints.txt -U qiskit[visualization] cvxpy
+    pip install -c constraints.txt pyscf
     sudo apt-get install -y pandoc graphviz
   displayName: 'Install dependencies'
 - bash: |

constraints.txt

@@ -0,0 +1 @@
+docplex==2.15.194