Allow Symfony 4

Author: nicolas-grekas

composer.json

@@ -17,7 +17,7 @@
     ],
     "require": {
         "php": ">=5.5.9",
-        "symfony/security-core": "~2.8|~3.0"
+        "symfony/security-core": "~2.8|~3.0|~4.0"
     },
     "require-dev": {
         "symfony/phpunit-bridge": "~2.8|~3.0",