add publish dir to gh-pages action

Author: trevorcampbell

.github/workflows/update_book.yml

@@ -32,5 +32,6 @@ jobs:
         uses: peaceiris/[email protected]
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./
           force_orphan: true 
           cname: python.datasciencebook.ca