Symfony yaml dependency added.

Author: dmitry-ivanov

composer.json

@@ -17,6 +17,7 @@
         "symfony/finder": "3.1.*",
         "symfony/process": "3.1.*",
         "symfony/var-dumper": "3.1.*",
+        "symfony/yaml": "3.1.*",
         "spatie/array-to-xml": "^2.2"
     },
     "require-dev": {