Document that checkSession requires a callback

[civility-bot]

Changes

Add the callback parameter required by checkSession to https://auth0.github.io/auth0.js/global.html#checkSession.

References

https://auth0.com/docs/libraries/auth0js/v9#using-checksession-to-acquire-new-tokens

Not sure where the signature of the callbacks are documented (e.g. authorizeCallback), so I've just followed the apparent naming convention and used checkSessionCallback. If that needs to be documented, another PR can do it.

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All tests and linters described in the Develop section run without errors

[stevehobbsdev]

Thanks!