Adds support for an optional 'partner_id' parameter in 'setAppInfo'

[zachwick]

This adds support for an optional partner_id attribute in the SetAppInfo hash.

[ob-stripe]

This looks good, but I wonder if the parameter should be called partnerId in the Node API (but still be serialized as partner_id).

cc @jlomas-stripe @brandur-stripe

[zachwick]

@ob-stripe @jlomas-stripe @brandur-stripe I'm open to changing the parameter name to whatever to match whatever conventions we already have in stripe-node. I used partner_id since that it what was used in most of the other Stripe API client libraries.

[brandur-stripe]

Hm, good points. Node's kind of a weird one because camel case is definitely the language convention, but we recommend that for this library's API methods, the plain snakecase parameter names be sent. For example:

      stripe.applePayDomains.create({
        domain_name: 'example.com',
      });

I could see the argument though that setAppInfo is more like a function than an API call, and its arguments are really arguments rather than API parameters, and therefore should take camelcase naming. I could go either way, but I'd probably lean toward leaving it as is here.

@jlomas-stripe Thoughts?

[remi-stripe]

@brandur-stripe @ob-stripe Just wanted to check back in on this PR!