corrected phpdoc

src/Symfony/Component/DependencyInjection/ContainerBuilder.php

@@ -547,7 +547,7 @@ class ContainerBuilder extends Container implements TaggedContainerInterface
      *
      * @param string $id The service identifier
      *
-     * @return Definition A Definition instance
+     * @return Alias An Alias instance
      *
      * @throws \InvalidArgumentException if the alias does not exist
      *