update demo dependency version

Author: nshen

demo/package.json

@@ -10,6 +10,6 @@
   "devDependencies": {
     "cesium": "^1.85.0",
     "vite": "^2.5.6",
-    "vite-plugin-cesium": "^1.2.6"
+    "vite-plugin-cesium": "^1.2.9"
   }
 }