根据选择器查询目标元素
@param {String} selector 选择器,用于 querySelectorAll
@param {HTMLElement} container 父容器
@param {Boolean} toArray 强制输出为数组
@return {NodeList|Array}
function query(selector) {
  var container = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : document;
  var toArray = arguments[2];

  var retNodeList = container.querySelectorAll(selector);
  return toArray ? _Array$from(retNodeList) : retNodeList;
}