Function isDateString

isDateString(str: string): boolean
验证日期字符串，允许中间用横杠或点连接。
Parameters
- str: string
Returns boolean
Since
0.0.1
Example
```
isDateString('2021-06-03')       // true
isDateString('1995.08.06')       // true
isDateString('2020-05.46')       // false
```
- Defined in format-validation.ts:699