Add optional responseKey to updateResource and fix updateCustomerAddress

[BrandonKerr]

When calling $this->shopify->updateCustomerAddress(...), I would get this error:

Undefined array key "address"

As per the docs, the response has customer_address and not address, as the code was looking for. I spotted that the createCustomerAddress function, and subsequently the createResource function made use of a specified response key of "customer_address". I simply applied the same logic for the update.