[docs] fix live example link (#5547)

Use https://aframe.io/aframe/examples/docs/360-gallery/ instead of https://aframe.io/examples/docs/360-gallery/

Author: TomoyaKuroda

docs/guides/building-a-360-image-gallery.md

@@ -9,7 +9,7 @@ examples:
     src: https://github.com/aframevr/aframe/tree/master/examples/docs/360-gallery/index.html
 ---
 
-[live-example]: https://aframe.io/examples/docs/360-gallery/
+[live-example]: https://aframe.io/aframe/examples/docs/360-gallery/
 
 ![360° Image Viewer](/images/docs/360-image-viewer.png)