code: function getCenter(touches) {
      var valuesX = [], valuesY = [];
  
      Hammer.utils.each(touches, function(touch) {
        // I prefer clientX because it ignore the scrolling position
        valuesX.push(typeof touch.clientX !== 'undefined' ? touch.clientX : touch.pageX );
        valuesY.push(typeof touch.clientY !== 'undefined' ? touch.clientY : touch.pageY );
      });
  
      return {
        pageX: ((Math.min.apply(Math, valuesX) + Math.max.apply(Math, valuesX)) / 2),
        pageY: ((Math.min.apply(Math, valuesY) + Math.max.apply(Math, valuesY)) / 2)
      };
    }
docs: get the center of all the touches
  @param   {Array}     touches
  @returns {Object}    center