update actions-gh-pages reference in docs

Author: timkpaine

docs/src/overview.md

@@ -49,7 +49,7 @@ jobs:
       - run: pip install yardang
       - run: yardang build
       - name: Deploy
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           publish_branch: gh-pages
           github_token: ${{ secrets.GITHUB_TOKEN }}