Error executing "composer update" in post-update-cmd

When launching a composer Update within a project, it shows me the following error:

  

Generating autoload files
  Illuminate \ Foundation \ ComposerScripts :: postUpdate
  php artisan optimize
  Php artisan script optimize handling the post-update-cmd event returned with error code 255

The project is this: link

In the file composer.json I have these scripts :

"scripts": {
        "post-root-package-install": [
            "php -r \"file_exists('.env') || copy('.env.example', '.env');\""
        ],
        "post-create-project-cmd": [
            "php artisan key:generate"
        ],
        "post-install-cmd": [
            "Illuminate\Foundation\ComposerScripts::postInstall",
            "php artisan optimize"
        ],
        "post-update-cmd": [
            "Illuminate\Foundation\ComposerScripts::postUpdate",
            "php artisan optimize"
        ]
    },

The version of Composer is 1.4.1

How can I solve it?