fix(example): add allow-downloads to iframe sandbox

Author: Hufe921

example/main/index.html

@@ -15,7 +15,7 @@ <h1>canvas-editor-plugin-example</h1>
         style="width:100%; height:80vh; border:0; border-radius: 4px; overflow:hidden;"
         title="nostalgic-grothendieck-fwm59s"
         allow="accelerometer; ambient-light-sensor; camera; encrypted-media; geolocation; gyroscope; hid; microphone; midi; payment; usb; vr; xr-spatial-tracking"
-        sandbox="allow-forms allow-modals allow-popups allow-presentation allow-same-origin allow-scripts"></iframe>
+        sandbox="allow-forms allow-modals allow-popups allow-presentation allow-same-origin allow-scripts allow-downloads"></iframe>
     </main>
   </div>
   <script type="module" src="/src/main.ts"></script>