update login kit usage example

[scifisatan]

the provided example didn't work for me

• enforcement of authResponse as the type TikTokAuthResponse was giving error as the was not syntactically correct
• the response doesn't have code prop, it's authCode
• the multi-line comment was also incorrect on error handling.

[CLAassistant]

All committers have signed the CLA.

[scifisatan]

@lollojjj just a reminder to check if we can merge this