docs: update linkdin provider documentation

[TilsonM17]

Recently I had an error when trying to do Sig In, the reason is that Linkdin changed the way it authenticates, and the package is already that way.

The old way to connect with provider givem error, because now LinkedIn is using Sign In with LinkedIn using OpenID Connect instead of Sign In with LinkedIn.

So you just need to use linkedin-openid instead of linkedin in the service.php and Socialite::driver('linkedin-openid')->redirect();

[atymic]

Are you sure this is correct?
https://github.com/SocialiteProviders/Providers/blob/master/src/LinkedIn/LinkedInExtendSocialite.php