[Yaml] Recommend using quotes instead of PARSE_KEYS_AS_STRINGS

Author: GuilhemN

Mapping/Loader/YamlFileLoader.php

@@ -15,7 +15,6 @@
 use Symfony\Component\Serializer\Mapping\AttributeMetadata;
 use Symfony\Component\Serializer\Mapping\ClassMetadataInterface;
 use Symfony\Component\Yaml\Parser;
-use Symfony\Component\Yaml\Yaml;
 
 /**
  * YAML File Loader.
@@ -114,7 +113,7 @@ private function getClassesFromYaml()
             $this->yamlParser = new Parser();
         }
 
-        $classes = $this->yamlParser->parse(file_get_contents($this->file), Yaml::PARSE_KEYS_AS_STRINGS);
+        $classes = $this->yamlParser->parse(file_get_contents($this->file));
 
         if (empty($classes)) {
             return array();