update to python 3.9 for dev build to fix importlib error

Author: marthacryan

.circleci/config.yml

@@ -314,7 +314,7 @@ jobs:
 
   plotlyjs_dev_build:
     docker:
-      - image: cimg/python:3.8-node
+      - image: cimg/python:3.9-node
         environment:
           LANG: en_US.UTF-8
     resource_class: large