Update deploy-demo.yml

Fix build error: Cannot find module 'ngx-diff2html'

Author: AXeL-dev

.github/workflows/deploy-demo.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Install and Build 🔧
         run: |
           npm install
-          npm run build:demo:github
+          npm run build && npm run build:demo:github
           cp dist/demo/index.html dist/demo/404.html
 
       - name: Deploy 🚀