title: Find all users with specific role using rolify
body: <p>How can i get all users with specific role when using rolify? I've tried the following but it didn't help:</p>
  
  <pre><code>User.with_role :admin
  </code></pre>
  
  <p>I get the following error: </p>
  
  <pre><code>NoMethodError: undefined method `with_role' for #&lt;Class:0x0000000743f9c0&gt;
  </code></pre>
  
  <p>Couldn't find any way to do this.</p>