Changed dependency

Author: msarca

composer.json

@@ -18,7 +18,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^6.5",
-        "symfony/yaml": "^4.1"
+        "symfony/yaml": "^3.4"
     },
     "autoload": {
         "psr-4": {