explain that a role can be an instance of Role

Only mentioning the RoleInterface seems to be confusing as it is
deprecated since Symfony 3.3.

src/Symfony/Component/Security/Core/Authentication/Token/AbstractToken.php

@@ -43,7 +43,7 @@ abstract class AbstractToken implements TokenInterface
             if (is_string($role)) {
                 $role = new Role($role);
             } elseif (!$role instanceof RoleInterface) {
-                throw new \InvalidArgumentException(sprintf('$roles must be an array of strings, or RoleInterface instances, but got %s.', gettype($role)));
+                throw new \InvalidArgumentException(sprintf('$roles must be an array of strings, Role instances or RoleInterface instances, but got %s.', gettype($role)));
             }
 
             $this->roles[] = $role;