refactor: remove loading attribute when zooming

Author: francoischalifour

src/medium-zoom.js

@@ -381,7 +381,7 @@ const mediumZoom = (selector, options = {}) => {
 
         // In Firefox, the `loading` attribute needs to be set to `eager` (default
         // value) for the load event to be fired.
-        active.zoomedHd.setAttribute('loading', '')
+        active.zoomedHd.removeAttribute('loading')
 
         // Wait for the load event of the hd image. This will fire if the image
         // is already cached.