fix: update demo site URL

Author: hsluoyz

README.md

@@ -13,7 +13,7 @@
 
 **Official Website: [https://www.casos.net](https://www.casos.net)**
 
-**Live Demo: [https://casos.casnode.com](https://casos.casnode.com)**
+**Live Demo: [https://demo.casos.net](https://demo.casos.net)**
 
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