Fix trailing comma in composer (closes symfony#4310)

Author: vierbergenlars

src/Symfony/Component/Validator/composer.json

@@ -16,7 +16,7 @@
         }
     ],
     "require": {
-        "php": ">=5.3.3",
+        "php": ">=5.3.3"
     },
     "require-dev": {
         "symfony/http-foundation": "2.1.*",