Removing duplicate line (#3578)

Removing duplicate line

lib/timeline/Core.js

@@ -76,7 +76,6 @@ Core.prototype._create = function (container) {
   this.dom.root.appendChild(this.dom.rightContainer);
   this.dom.root.appendChild(this.dom.top);
   this.dom.root.appendChild(this.dom.bottom);
-  this.dom.root.appendChild(this.dom.bottom);
   this.dom.root.appendChild(this.dom.rollingModeBtn);
 
   this.dom.centerContainer.appendChild(this.dom.center);