Fix one dependency requirement

Author: nicolas-grekas

composer.json

@@ -20,7 +20,7 @@
     },
     "require-dev": {
         "symfony/phpunit-bridge": "~2.7",
-        "symfony/yaml": "~2.0",
+        "symfony/yaml": "~2.0,>=2.0.5",
         "symfony/config": "~2.2",
         "symfony/property-access": "~2.3",
         "doctrine/annotations": "~1.0",