Use PSR logger interface

The Symfony logger interface does not seem to exist anymore (it was
probably made useless by the PSR logger).

Tests/Translator/Extractor/JMSTranslatorBundle/AdminExtractorTest.php

@@ -70,7 +70,7 @@ class AdminExtractorTest extends \PHPUnit_Framework_TestCase
                 return;
             }));
 
-        $logger = $this->getMock('Symfony\Component\HttpKernel\Log\LoggerInterface');
+        $logger = $this->getMock('Psr\Log\LoggerInterface');
 
         $this->pool = new Pool($container, '', '');
         $this->pool->setAdminServiceIds(array('foo_admin', 'bar_admin'));

Translator/Extractor/JMSTranslatorBundle/AdminExtractor.php

@@ -15,11 +15,11 @@ use JMS\TranslationBundle\Model\FileSource;
 use JMS\TranslationBundle\Model\Message;
 use JMS\TranslationBundle\Model\MessageCatalogue;
 use JMS\TranslationBundle\Translation\ExtractorInterface;
+use Psr\Log\LoggerInterface;
 use Sonata\AdminBundle\Admin\AdminInterface;
 use Sonata\AdminBundle\Admin\Pool;
 use Sonata\AdminBundle\Security\Handler\SecurityHandlerInterface;
 use Sonata\AdminBundle\Translator\LabelTranslatorStrategyInterface;
-use Symfony\Component\HttpKernel\Log\LoggerInterface;
 use Symfony\Component\Translation\TranslatorInterface;
 
 class AdminExtractor implements ExtractorInterface, TranslatorInterface, SecurityHandlerInterface, LabelTranslatorStrategyInterface