Downgrade symfony/http-foundation to temporary fix session persistence issues

This is a temporary fix for https://github.com/laravel/framework/issues/4441 to fix newly introduced session persistence issues when using a composer minimum-stability of dev.

Currently, any new Laravel project cloned from the `dev` branch will be unable to persist sessions in the database due to the reasons outlined in https://github.com/laravel/framework/issues/4441.