坑 Dayjs 多加一天
/**
* Returns a cloned Day.js object with a specified amount of time added.
* ```
* dayjs().add(7, 'day')// => Dayjs
* ```
* Units are case insensitive, and support plural and short forms.
*
* Docs: https://day.js.org/docs/en/manipulate/add
*/
add(value: number, unit?: ManipulateType): Dayjs
查看接口说明add 返回的 Dayjs 对象,需要再调用其Format的转换将其转换成为 String对象