Use new repository structure

composer.json

 {
-    "name": "phpbenchmarks/symfony",
+    "name": "phpbenchmarks/symfony-common",
     "license": "proprietary",
     "type": "project",
     "autoload": {
         }
     },
     "require": {
-        "php": ">=5.4.0"
+        "symfony/symfony": "^2.3"
     }
 }