fixed vue3 example

Author: adumesny

demo/vue3js.html

@@ -29,8 +29,7 @@ <h1>How to integrate GridStack.js with Vue.js</h1>
       <section class="grid-stack"></section>
     </main>
     <script type="module">
-      import { createApp } from "https://cdn.jsdelivr.net/npm/vue@3.0.0/dist/vue.esm-browser.js";
-      import { ref, onMounted } from "vue";
+      import { createApp, ref, onMounted } from "https://cdn.jsdelivr.net/npm/vue@3.0.11/dist/vue.esm-browser.js";
 
       createApp({
         setup() {