Remove from <img> the srcset attribute if present to actually show hi…

…-res image when zoomed-in

…and put it back when zoomed-out

build/zooming.js

@@ -442,6 +442,7 @@ var target = {
     this.el = el;
     this.instance = instance;
     this.srcThumbnail = this.el.getAttribute('src');
+    this.srcset = this.el.getAttribute('srcset');
     this.srcOriginal = getOriginalSource(this.el);
     this.rect = this.el.getBoundingClientRect();
     this.translate = null;
@@ -515,20 +516,30 @@ var target = {
 
       // Force compute the hi-res image in DOM to prevent
       // image flickering while updating src
+      if (this.srcset) {
+        temp.setAttribute('srcset', '');
+      }
       temp.setAttribute('src', this.srcOriginal);
       temp.style.position = 'fixed';
       temp.style.visibility = 'hidden';
       parentNode.appendChild(temp);
 
       // Add delay to prevent Firefox from flickering
       setTimeout(function updateSrc() {
+        if (this.srcset) {
+          this.el.setAttribute('srcset', '');
+        }
         this.el.setAttribute('src', this.srcOriginal);
+
         parentNode.removeChild(temp);
       }.bind(this), 50);
     }
   },
   downgradeSource: function downgradeSource() {
     if (this.srcOriginal) {
+      if (this.srcset) {
+        this.el.setAttribute('srcset', this.srcset);
+      }
       this.el.setAttribute('src', this.srcThumbnail);
     }
   },