changed composite key order, the same as in join conditions

doc/translatable.md

@@ -632,7 +632,7 @@ use Gedmo\Translatable\Entity\MappedSuperclass\AbstractTranslation;
 
 /**
  * @ORM\Table(name="article_translations", indexes={
- *      @ORM\index(name="article_translation_idx", columns={"locale", "object_class", "foreign_key", "field"})
+ *      @ORM\index(name="article_translation_idx", columns={"locale", "object_class", "field", "foreign_key"})
  * })
  * @ORM\Entity(repositoryClass="Gedmo\Translatable\Entity\Repository\TranslationRepository")
  */