Fix for C2 country code for China

[jtapia]

Summary

As selecting China from PayPal addresses, the country_code that we received is C2, and that doesn't match with the Carmen/Spree::Country default code for China(CN)

=> #<ActionController::Parameters {"city"=>"Beijing", "state"=>"BEIJING", "country_code"=>"C2", "postal_code"=>"100000"} permitted: false>

[kennyadsl]

@jtapia can you please rebase this one? The failure should be gone now, thanks!