Change translation request for postgresql platform fix #1168

Hi, 
i've posted #1168 2 weeks ago, and here is a little fix for this

Use case: 
Postgresql 9.3 

Something like that: 

$qv = $this->getEntityManager()->createQuery($dqlValidities);
        //There is a bug in TranslatbleGedmo Behaviour
        //follow up: https://github.com/Atlantic18/DoctrineExtensions/issues/1168
        $qv->setHint(
            \Doctrine\ORM\Query::HINT_CUSTOM_OUTPUT_WALKER,
            'Gedmo\\Translatable\\Query\\TreeWalker\\TranslationWalker'
        );
        $qv->setHint(TranslatableListener::HINT_TRANSLATABLE_LOCALE,$locale);

was failing because of type difference between foreign_key field and the generated query.

This pr solve that.

Thanks