FIX: update sphinx-tojupyter to support sphinxv4

Author: mmcky

environment.yml

@@ -8,7 +8,7 @@ dependencies:
   - pip:
     - jupyter-book==0.12.0
     - quantecon-book-theme==0.2.7
-    - sphinx-tojupyter==0.1.2
+    - sphinx-tojupyter==0.2.0
     - sphinxext-rediraffe==0.2.7
     - sphinx-exercise==0.2.1
     - ghp-import==1.1.0