Fatal errors with fresh Drupal 8.4 (Symfony 3.x)

This one in line 22:
Fatal error: Declaration of Drupal\geofield\Plugin\Validation\Constraint\GeoConstraint::initialize(Symfony\Component\Validator\ExecutionContextInterface $context) must be compatible with Symfony\Component\Validator\ConstraintValidatorInterface::initialize(Symfony\Component\Validator\Context\ExecutionContextInterface $context) in /var/www/sf/htdocs/modules/contrib/geofield/src/Plugin/Validation/Constraint/GeoConstraint.php on line 22

In the symfony/validator/CHANGELOG.md I see a Backwards compatibility BREAK:
* [BC BREAK] `ConstraintValidatorInterface::initialize` is now type hinted against `ExecutionContextInterface` instead of `ExecutionContext`

I think the solution is to just replace the type hint class with it's interface. It makes sense to type hint on the interface instead of a class.
This way the class will be swappable with another class that implements the same interface.

Version 8.x-1.0-alpha4 seems to fix this in my case.

Same here version 8.x-1.0-alpha4 fixed the issue for me.

Hello,

if I use composer to install this module I get the alpha 1 version. How to get the last version with composer ?

Thanks.