Update composer.json

Use same PHP version as for Symfony component to match its requirements.

composer.json

@@ -12,7 +12,7 @@
         }
     ],
     "require": {
-        "php": ">=5.3.0",
+        "php": ">=5.3.2",
         "symfony/event-dispatcher": "2.*"
     },
     "autoload": {