Actually lookup the card token on customer update

I needed this because I want to test that I'm actually updating the card. Didn't bother adding any test for this because..

1. I know it's working as I expected in my actual tests for my app
2. this doesn't break the existing tests
3. at worst this is just replacing a random behaviour with another random behaviour
4. not sure if you want to mix in the token generation/lookup stuff in the customers tests