Bump Pygments to 2.8.1

.github/workflows/gh-pages.yml

@@ -11,7 +11,7 @@ jobs:
         run: |
           sudo apt-get -y update
           sudo apt-get -y install python3-pip
-          pip install mkdocs-material pygments mkdocs-redirects
+          pip install mkdocs-material pygments==2.8.1 mkdocs-redirects
           mkdocs build --verbose --clean
 
       - name: Deploy 🚀