Optimize autoload prefix in composer.json

By having more specific autoload prefixes it is possible to reduce the
number of stat calls made. Also it prevents conflicts with similar
namespaces.

Author: Slamdunk

composer.json

@@ -19,7 +19,7 @@
         "php": ">=5.3.3"
     },
     "autoload": {
-        "psr-0": { "Symfony\\Component\\Serializer": "" }
+        "psr-0": { "Symfony\\Component\\Serializer\\": "" }
     },
     "target-dir": "Symfony/Component/Serializer",
     "minimum-stability": "dev",