force old mistune for website

Summary: When parsing tutorials for building the website, we fix a few libraries at old versions. They need mistune 0.8.4, not the new version 2+, so this gets added to the list of fixed-version libraries.

Reviewed By: patricklabatut

Differential Revision: D33236031

fbshipit-source-id: 2b152b64043edffc59fa909012eab5794c7e8844

scripts/publish_website.sh

@@ -32,7 +32,7 @@ conda create -y -n myenv python=3.7 nodejs
 # is what lets conda activate work so smoothly.
 
 conda activate myenv
-pip install nbformat==4.4.0 nbconvert==5.3.1 ipywidgets==7.5.1 tornado==4.2 bs4 notebook==5.7.12
+pip install nbformat==4.4.0 nbconvert==5.3.1 ipywidgets==7.5.1 tornado==4.2 bs4 notebook==5.7.12 'mistune<2'
 npm install --global yarn
 
 cd /loc