validateDate method
Checks whether or not the {@link #expMonth} and {@link #expYear} fields represent a valid expiry date.
@return {@code true} if valid, {@code false} otherwise
Implementation
bool validateDate() {
return _ccValidator
.validateExpDate(
'${expMonth.toString().padLeft(2, '0')}/${expYear.toString().padLeft(2, '0')}')
.isValid;
}