GoutteServiceProvider.php

<?php

namespace Caefer;

use Silex\Application;
use Silex\ServiceProviderInterface;
use Goutte\Client;

class GoutteServiceProvider implements ServiceProviderInterface
{
    public function register(Application $app)
    {   
        $app['goutte.client'] = $app->share(function () use ($app) {
            return new Client();
        }); 

        if (isset($app['goutte.class_path'])) {
            $app['autoloader']->registerNamespaces(array(
                'Goutte' => $app['goutte.class_path'],
                'Zend'   => $app['goutte.class_path'].'/../vendor/zend/library',
            ));
        }   
    }   
}

need add
public function boot(Application $app)
{ }