The Laravel Socialite uses Google+ API to authenticate user, but since Google+ API is shutting down, the https://www.googleapis.com/plus/v1/people/me will no longer works.
If you are currently using Google+ API for Socialite Google OAuth2 authentication, you should upgrade Socialite version 4.
If are stuck with Socialite version 3.x because you need to run Laravel with lower or equal to version 5.5 (or because of PHP 7.0), change the composer package to 3.0.x-dev and run
composer update as of this writing.
I am expecting Laravel Socialite 3.x Google OAuth API will be updated soon, but the package has not yet released.