luhn: Update tests and example#409

Merged

behrtam merged 5 commits intoexercism:masterfrom

rootulp:luhn/tests

Mar 9, 2017

Commits on Jan 29, 2017

luhn: Update tests
Rootul Patel
committed
luhn: Update example to satisfy new tests
Rootul Patel
committed

Commits on Feb 27, 2017

luhn: Add canonical tests
Rootul Patel
committed

Commits on Mar 8, 2017

luhn: Add test_is_valid_can_be_called_repeatedly
Rootul Patel
committed
luhn: Use a_valid_Canadian_SIN for last test
Rootul Patel
committed