Error in accessing to php artisan tinker

Hello Everyone, I am new in Laravel framework and I am using XAMPP 7.0 with PHP 7.0 I am getting through with Jeffry Way tutorials and in Eloquent chapter, I can't open php artisan tinker tool and when I am trying, the error occurs as follow:

PHP Fatal error: Cannot use PhpParser\Node\Scalar\String as String because 'String' is a special class name in C:\xampp\htdocs\learning-laravel\vendor\psy\psysh\src\Psy\CodeCleaner\MagicConstantsPass.php on line 19

[Symfony\Component\Debug\Exception\FatalErrorException] Cannot use PhpParser\Node\Scalar\String as String because 'String' is a special class name

Anyone can help as soon as he/she can. Thanks.