Allow Symfony 4.0

Author: piotrantosik

composer.json

@@ -17,7 +17,7 @@
     "require": {
         "php"             : ">=5.3.0",
         "monolog/monolog" : "~1.6",
-        "symfony/yaml"    : "~2.3|~3.0"
+        "symfony/yaml"    : "~2.3|~3.0|~4.0"
     },
     "autoload": {
         "psr-4": { "EasyCorp\\EasyLog\\": "src" }