log dither output

.github/workflows/deploy.yml

@@ -33,7 +33,7 @@ jobs:
         env:
           ROOT: ${{ github.workspace }}/content
           KEY: ${{ github.workspace }}/secret.key
-        run: cd bin/dither && bundle exec ruby dither.rb &
+        run: cd bin/dither && bundle exec ruby dither.rb >> dither.log 2>&1 &
 
       - name: Test build
         env:
@@ -59,3 +59,9 @@ jobs:
         env:
           SERVER_IP: ${{ secrets.SERVER_IP }}
         run: bin/deploy
+
+      - name: Upload dither.log
+        uses: actions/upload-artifact@v3
+        with:
+          name: dither.log
+          path: bin/dither/dither.log