Update deprecated OAuth renew_token method

[square]

Update deprecated OAuth renew_token method

[StephenJosey]

Can you clarify what you mean? The RenewToken endpoint is marked as deprecated in the docs (https://github.com/square/square-ruby-sdk/blob/master/doc/api/o-auth.md) for this SDK. Furthermore, it's not needed; you now use ObtainToken for refreshing tokens.

[georgewambold]

@StephenJosey Ahh you're right. That's my mistake. I thought you had deprecated the RenewToken endpoint without replacing it, I didn't realize that you could use ObtainToken for renewing tokens.

Thanks for the prompt response 👍🏼

edit: Maybe the documentation could be clearer that the ObtainToken method is now used in place of the old RenewToken method? The documentation currently links to the OAuth Walkthrough which uses cURL, so I just assumed we had to make the request manually.