swipeUp = function swipeUp(selector, yOffset, speed) {
  /**
   * we can't use default values for function parameter here because this would
   * break the ability to chain the command with an element if reverse is used
   */
  yOffset = typeof yOffset === 'number' ? yOffset : -100;
  speed = typeof speed === 'number' ? speed : 100;

  /**
   * make sure yoffset is negative so we scroll down
   */
  yOffset = yOffset > 0 ? yOffset * -1 : yOffset;

  return this.pause(100).swipe(selector, 0, yOffset, speed);
}
Perform a swipe up on an element.

@alias browser.swipeUp
@param {String} selector  element to swipe on
@param {Number=} yoffset    y offset of swipe gesture (in pixels or relative units)
@param {Number} speed     time (in seconds) to spend performing the swipe
@uses mobile/swipe
@type mobile