code: function getSpecificity(selectorText) {
      return specificity
          .calculate(selectorText)[0]
          .specificity
          .split(',')
          .map(function(s) {
              return parseInt(s, 10);
          });
  }
docs: 获取优先级信息
  @param   {String}    选择器文本
  @return  {Array}