title: composer require laravel/passport not working in laravel 5.8
body: <p>I'm using Laravel 5.8 although <code>6.0.3</code> is available. I'm using it because the tutorial I'm following is using Laravel 5.8.</p>
  
  <p>When, I command:  </p>
  
  <pre class="lang-sh prettyprint-override"><code>composer require laravel/passport
  </code></pre>
  
  <p>it throws an error</p>
  
  <blockquote>
    <p>Your requirements could not be resolved to an installable set of packages.</p>
    
    <p>Problem 1
        - Conclusion: remove laravel/framework v5.8.35
        - Conclusion: don't install laravel/framework v5.8.35
        - laravel/passport 8.x-dev requires illuminate/encryption ^6.0|^7.0 -> satisfiable by illuminate/encryption[6.x-dev, 7.0.x-dev, v6.0.0, v6.0.1, v6.0.2, v6.0.3, v6.0.4, v6.1.0, v6.2.0, v6.3.0, v6.4.1].
        - laravel/passport v8.0.0 requires illuminate/encryption ^6.0|^7.0 -> satisfiable by illuminate/encryption[6.x-dev, 7.0.x-dev, v6.0.0, v6.0.1, v6.0.2, v6.0.3, v6.0.4, v6.1.0, v6.2.0, v6.3.0, v6.4.1].
        - don't install illuminate/encryption 6.x-dev|don't install laravel/framework v5.8.35
        - don't install illuminate/encryption 7.0.x-dev|don't install laravel/framework v5.8.35
        - don't install illuminate/encryption v6.0.0|don't install laravel/framework v5.8.35
        - don't install illuminate/encryption v6.0.1|don't install laravel/framework v5.8.35
        - don't install illuminate/encryption v6.0.2|don't install laravel/framework v5.8.35
        - don't install illuminate/encryption v6.0.3|don't install laravel/framework v5.8.35
        - don't install illuminate/encryption v6.0.4|don't install laravel/framework v5.8.35
        - don't install illuminate/encryption v6.1.0|don't install laravel/framework v5.8.35
        - don't install illuminate/encryption v6.2.0|don't install laravel/framework v5.8.35
        - don't install illuminate/encryption v6.3.0|don't install laravel/framework v5.8.35
        - don't install illuminate/encryption v6.4.1|don't install laravel/framework v5.8.35
        - Installation request for laravel/framework (locked at v5.8.35, required as 5.8.*) -> satisfiable by laravel/framework[v5.8.35].
        - Installation request for laravel/passport ^8.0 -> satisfiable by laravel/passport[8.x-dev, v8.0.0].</p>
    
    <p>Installation failed, reverting ./composer.json to its original content.</p>
  </blockquote>