User symfony/yaml 2.8.0.

Author: bgaillard

composer.json

@@ -44,6 +44,7 @@
 		"satooshi/php-coveralls" : "~0.6",
 		"sebastian/phpcpd" : "~2.0",
 		"squizlabs/php_codesniffer" : "~2.3",
-		"symfony/stopwatch" : "2.8.0"
+		"symfony/stopwatch" : "2.8.0",
+		"symfony/yaml" : "2.8.0"
 	}
 }