update composer.json

Author: MasaakiYoshida

composer.json

@@ -12,7 +12,7 @@
     ],
     "require": {
         "php": ">=5.3.9",
-        "phpmentors/workflower": "~1.2",
+        "phpmentors/workflower": "dev-symfony5",
         "symfony/config": "~4.0 || ~5.0",
         "symfony/dependency-injection": "~4.0 || ~5.0",
         "symfony/finder": "~4.0 || ~5.0",