onReleaseEnd = function onReleaseEnd() {
          listen(target$$1, 'transitionend', onReleaseEnd, false);
          _this3.lock = false;
          _this3.released = true;
          cb(target$$1);
        }
Release the Element currently grabbed.
@param  {Function} [cb=this.options.onRelease] A callback function that
will be called when a target is released and transition has ended. It
will get the target element as the argument.
@return {this}