Bump gh pages deploy actions versions

Author: marko-radosavljevic

.github/workflows/deploy-gh-pages.yaml

@@ -14,14 +14,14 @@ jobs:
       - uses: actions/checkout@v2
 
       - name: Setup mdBook
-        uses: peaceiris/actions-mdbook@v1
+        uses: peaceiris/actions-mdbook@v1.2.0
         with:
           mdbook-version: 'latest'
 
       - run: mdbook build
 
       - name: Deploy
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v3.9.1
         if: ${{ github.ref == 'refs/heads/master' }}
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}