Luhn Algorithm is not working as expected

[andreshndz]

Bug

Output of python -c "import pydantic.utils; print(pydantic.utils.version_info())":

             pydantic version: 1.3
            pydantic compiled: False
                 install path: /Users/andreshernandez/Desktop/git/pydantic/pydantic
               python version: 3.7.5 (default, Nov  1 2019, 02:16:32)  [Clang 11.0.0 (clang-1100.0.33.8)]
                     platform: Darwin-18.2.0-x86_64-i386-64bit
     optional deps. installed: ['typing-extensions', 'email-validator', 'devtools']

from pydantic.types import PaymentCardNumber

card_number = '4951486642583068'  # luhn valid
PaymentCardNumber(card_number).validate_luhn_check_digit(card_number)

Throws a LuhnValidationError:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.7/site-packages/pydantic/types.py", line 657, in validate_luhn_check_digit
    raise errors.LuhnValidationError
pydantic.errors.LuhnValidationError: card number is not luhn valid