Laravel composer update error: Nothing to install or update
<p>When I run composer update, I get the following error:</p>

<blockquote>
  <p>Loading composer repositories with package information
  Updating dependencies (including require-dev)
  Nothing to install or update
  Generating autoload files
  Illuminate\Foundation\ComposerScripts::postUpdate
  php artisan optimize
    [Symfony\Component\Debug\Exception\FatalErrorException]
    Class 'Laravel\Cashier\CashierServiceProvider' not found
  Script php artisan optimize handling the post-update-cmd event returned with err
  or code 255</p>
</blockquote>

<p>I put this code on the app.php file </p>

<blockquote>
  <p>Laravel\Cashier\CashierServiceProvider::class,</p>
</blockquote>

<p>and in the composer.json I also put this </p>

<blockquote>
  <p>"laravel/cashier": "~6.0"</p>
</blockquote>

<p>like in the laravel doc</p>

<p><a href="http://i.stack.imgur.com/8eWLx.png" rel="nofollow">stack errot</a></p>