try to change python version to build doc

Author: emmanuelle

.circleci/config.yml

@@ -374,7 +374,7 @@ jobs:
     docker:
       # specify the version you desire here
       # use `-browsers` prefix for selenium tests, e.g. `3.6.1-browsers`
-      - image: circleci/python:3.6.8-node
+      - image: circleci/python:3.7-node
 
         working_directory: ~/project