title: Plugin not loaded in CakePHP 3.7.1
body: <p>I have create custom plugin with name "Administrator" inside plugin folder. I have also add folder required. I have add following code:</p>
  
  <p>Inside : <strong>plugins/Administrator/config/route.php</strong></p>
  
  <pre><code>use Cake\Routing\Route\DashedRoute;
  use Cake\Routing\Router;
  Router::plugin(
      'Administrator',
         ['path' =&gt; '/admin'],
         function ($routes) {
            $routes-&gt;fallbacks(DashedRoute::class);
         }
    );
  </code></pre>
  
  <p>Inside : <strong>src/Application.php</strong></p>
  
  <pre><code>$this-&gt;addPlugin('Administrator', ['routes' =&gt; true]);
  </code></pre>
  
  <p>Inside : <strong>config/route.php</strong></p>
  
  <pre><code>$routes-&gt;scope('/admin', function ($routes) {
      $routes-&gt;loadPlugin('Administrator');
  });
  </code></pre>
  
  <p>Inside browser when I enter <a href="http://localhost/c3app/admin/users" rel="nofollow noreferrer">http://localhost/c3app/admin/users</a> </p>
  
  <p>It shows error "<strong>Error: AdminController could not be found.</strong> "</p>
  
  <p>I have added code in <strong>composer.json</strong> file</p>
  
  <pre><code> "autoload": {
      "psr-4": {
          "App\\": "src/",
          "Administrator" : "./plugins/Administrator/src"
      }
  },
  "autoload-dev": {
      "psr-4": {
          "App\\Test\\": "tests/",
          "Cake\\Test\\": "vendor/cakephp/cakephp/tests/",
          "Administrator" : "./plugins/Administrator/src"
      }
  },
  </code></pre>