Updated the Symfony components to version >= 4.0

Author: Willem Oostendorp

composer.json

@@ -5,9 +5,9 @@
     "license": "MIT",
     "require": {
         "php": ">=5.5.9",
-        "symfony/workflow": "^3.3",
-        "symfony/process": "^3.3",
-        "symfony/event-dispatcher": "^3.3",
+        "symfony/workflow": "^4.0",
+        "symfony/process": "^4.0",
+        "symfony/event-dispatcher": "^4.0",
         "illuminate/console": "5.3.* | 5.4.* | 5.5.* | 5.6.*",
         "illuminate/support": "5.3.* | 5.4.* | 5.5.* | 5.6.*"
     },