Symfony 4 compatibility. (#9)

Author: Vinorcola

composer.json

@@ -26,8 +26,8 @@
         "php": ">=5.6.0",
         "portphp/portphp": "^1.0.0",
         "seld/signal-handler": "^1.0",
-        "symfony/property-access": "^2.3 || ^3.0",
-        "symfony/validator": "^2.5 || ^3.0"
+        "symfony/property-access": "^2.3 || ^3.0 || ^4.0",
+        "symfony/validator": "^2.5 || ^3.0 || ^4.0"
     },
     "autoload": {
         "psr-4": {