Add symfony 4 compatibility

closes GH-53

Author: devbdaily

composer.json

@@ -13,7 +13,7 @@
     "require": {
         "phpunit/php-file-iterator": "~1.4",
         "monolog/monolog": "~1.7",
-        "symfony/console": "~2.1|~3.0"
+        "symfony/console": "~2.1|~3.0|~4.0"
     },
     "require-dev": {
         "phpunit/phpunit": "5.7.*",