Describe the bug
Using the 81* range UNION Pay card numbers does not pass isCreditCard check

Examples
Sample Test Cards: https://docs.adyen.com/development-resources/test-cards/test-card-numbers#china-unionpay

validator.isCreditCard('8171999900000000021')
false

The problem is the initial regex in https://github.com/validatorjs/validator.js/blob/master/src/lib/isCreditCard.js#L4

Additional context
Validator.js version: 13.6.0
Node.js version: 14
OS platform:l inux