code: function(duration, callback) {
        return this.each(function(index, el) {
          u(el).scrollTo(0, duration, callback);
        });
      }
docs: scrollToTop method
  shortcut for scroll to 0
  @param  {number}   duration - duration for the animation
  @param  {function} callback - function to call when finished
  @return {object}   this