title: Laravel 'with' and nested relation
body: <p>I am retrieving some relationship:</p>
  
  <pre><code>$requirements = Requirement::with([
              'countryMatch',
              'applier',
              'doc' ])-&gt;get();
  </code></pre>
  
  <p>and my model Requirements contains:</p>
  
  <pre><code>public function doc()
  {
      return $this-&gt;belongsTo(Doc::class);
  }
  </code></pre>
  
  <p>Right now all fine.</p>
  
  <p>Since my Doc model has its own relationship:</p>
  
  <pre><code>public function translation($language = null)
  {
      if ($language == null) {
          $language = /*App::getLocale()*/'en';
      }
      return $this-&gt;hasMany('App\DocTranslation')-&gt;where('language', '=', $language);
  }
  </code></pre>
  
  <p>I would like to retrieve this relationship direct in the first 'with' statement, something like this:</p>
  
  <pre><code>$requirements = Requirement::with([
          'countryMatch',
          'applier',
          'doc-&gt;translation()' ])-&gt;get();
  </code></pre>
  
  <p>but I receive error:</p>
  
  <pre><code>Call to undefined relationship [doc-&gt;translation()] on model [App\Requirement].
  </code></pre>
  
  <p>That's because relation translation is in Doc model not in Requirement.</p>