Support for Symfony 4 (php-debugbar#370)

Author: Nyholm

composer.json

@@ -19,7 +19,7 @@
     "require": {
         "php": ">=5.3.0",
         "psr/log": "^1.0",
-        "symfony/var-dumper": "^2.6|^3.0"
+        "symfony/var-dumper": "^2.6|^3.0|^4.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^4.0|^5.0"