(#179) Bump deploy actions

Author: colinangusmackay

.github/workflows/gh-pages.yml

@@ -47,7 +47,7 @@ jobs:
           destination: ./_site
 
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v1
+        uses: actions/upload-pages-artifact@v3
 
   # Deployment job
   deploy:
@@ -59,4 +59,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v2
+        uses: actions/deploy-pages@v4