Added symfony/yaml to Fix #154, #155

Added symfony/yaml to composer.json.

Author: ashtru

composer.json

@@ -14,7 +14,8 @@
         "goetas/xsd2php": "^2.0", 
         "goetas-webservices/xsd2php-runtime":"^0.2",
         "goetas-webservices/xsd-reader": "^0.1",
-        "jms/serializer": "serializer-master-dev as 1.0"
+        "jms/serializer": "serializer-master-dev as 1.0",
+        "symfony/yaml": "^3.1"
     },
     "require-dev": {
         "phpunit/phpunit": "~4.0",