Fixed doc CD (#15)

Use the Docker images repo from the emacs-lsp organization.

Author: jcs090218

.github/workflows/docs.yml

@@ -13,7 +13,8 @@ jobs:
       - name: MkDocs
         run: |
           cp -rf README.md images docs
-          docker run --rm -v ${PWD}:/docs squidfunk/mkdocs-material -- build
+          docker login docker.pkg.github.com --username $GITHUB_ACTOR --password ${{ secrets.GITHUB_TOKEN }}
+          docker run --rm -v ${PWD}:/docs docker.pkg.github.com/emacs-lsp/docs-image/docs-image -- build
 
       - name: Deploy
         uses: peaceiris/actions-gh-pages@v3