[WIP] Debug doc build memory error (#295)

* change doker type

* try avoid memory error

* remove medium+ because no money

* remove medium+ because no money

.circleci/config.yml

@@ -5,6 +5,7 @@ jobs:
     build_docs:
       docker:
         - image: cimg/python:3.9
+      resource_class: medium
       steps:
         - checkout
         - run:
@@ -39,7 +40,7 @@ jobs:
             command: |
               python -m pip install --user --upgrade --progress-bar off pip
               python -m pip install --user -e .
-              python -m pip install --user --upgrade --progress-bar off -r requirements.txt
+              python -m pip install --user --upgrade --no-cache-dir --progress-bar off -r requirements.txt 
               python -m pip install --user --upgrade --progress-bar off -r docs/requirements.txt
               python -m pip install --user --upgrade --progress-bar off ipython "https://api.github.com/repos/sphinx-gallery/sphinx-gallery/zipball/master" memory_profiler