Add shipping to the charge object

R: @jimdanz || @berg 
cc: @anurag 

The charge object[0] has a shipping field, but stripe-java wasn't updated to reflect the change.

[0] https://stripe.com/docs/api#charge_object
Correct me if I'm wrong but I don't think that we provide generated equals/hashcode methods in our other model classes.  Are you deliberately trying to introduce that for new classes?  Maybe a separate step of adding generated equals / hashcode everywhere would be better.