update documentation to use appInfo

[christianaranda]

This request updates the documentation to use the correct way to send appInfo, taken from the PR found here:

The current documentation references a deprecated method stripe.setAppInfo({}) for setting appInfo on requests. Using the current documentation results in this error:

stripe.appInfo({
       ^

TypeError: stripe.appInfo is not a function
    at Object.<anonymous> (/Users/caranda/Documents/Ignitio/repositories/stripe-collector/index.js:7:8)
    at Module._compile (node:internal/modules/cjs/loader:1101:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1153:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:17:47

[CLAassistant]

All committers have signed the CLA.

[richardm-stripe]

Thank you for the contribution!