title: Mail::queue not working
body: <p>i'm unable to queue emails in laravel 5.4. in previous laravel 5.3 projects all worked fine.</p>
  
  <p>Send is still working:</p>
  
  <pre><code>Mail::send('email.blank', ['title' =&gt; 'nice', 'content' =&gt; 'message'], function ($message)
          {
              $message-&gt;from('a@b.com', 'test');
              $message-&gt;to('a@b.com');
          });
  </code></pre>
  
  <p>Queue does not work:</p>
  
  <pre><code>Mail::queue('email.blank', ['title' =&gt; 'nice', 'content' =&gt; 'message'], function ($message)
          {
              $message-&gt;from('a@b.com', 'test');
              $message-&gt;to('a@b.com');
          });
  </code></pre>
  
  <p>With the following error:</p>
  
  <pre><code>InvalidArgumentException in Mailer.php line 314:
  Only mailables may be queued.
  in Mailer.php line 314
  at Mailer-&gt;queue('email.blank', array('title' =&gt; 'nice', 'content' =&gt; 'message'), object(Closure)) in Facade.php line 221
  at Facade::__callStatic('queue', array('email.blank', array('title' =&gt; 'nice', 'content' =&gt; 'message'), object(Closure))) in EmailController.php line 16
  at EmailController-&gt;mailtest()
  at call_user_func_array(array(object(EmailController), 'mailtest'), array()) in Controller.php line 55
  at Controller-&gt;callAction('mailtest', array()) in ControllerDispatcher.php line 44
  at ControllerDispatcher-&gt;dispatch(object(Route), object(EmailController), 'mailtest') in Route.php line 203
  at Route-&gt;runController() in Route.php line 160
  at Route-&gt;run() in Router.php line 559
  at Router-&gt;Illuminate\Routing\{closure}(object(Request)) in Pipeline.php line 30
  at Pipeline-&gt;Illuminate\Routing\{closure}(object(Request)) in SubstituteBindings.php line 41
  at SubstituteBindings-&gt;handle(object(Request), object(Closure)) in Pipeline.php line 148
  at Pipeline-&gt;Illuminate\Pipeline\{closure}(object(Request)) in Pipeline.php line 53
  </code></pre>
  
  <p>I've created the queue table by</p>
  
  <pre><code>php artisan queue:table
  php artisan migrate
  </code></pre>
  
  <p>and changed the driver to database</p>
  
  <p><strong><em>UPDATE</em></strong>
  it looks like in laravel 5.4 you are only able to queue emails using mailables</p>
  
  <pre><code>php artisan make:mail TestMail
  </code></pre>
  
  <p>within the newly created class change the build function to return an existing view e.g</p>
  
  <pre><code>public function build()
      {
          return $this-&gt;view('email.test');
      }
  </code></pre>
  
  <p>then queue the mail</p>
  
  <pre><code> Mail::to('a@b.com')-&gt;send(new TestMail());
  </code></pre>
  
  <p>thanks</p>