title: Get the current category slug in Wordpress / Timber
body: <p>In my <code>Single.php</code> I'm trying to get the current posts category slug:</p>
  
  <pre><code>$category = get_category(get_query_var('cat'));
  $cat_slug = $category-&gt;slug;
  </code></pre>
  
  <p>But it doesn't return anything. And there's definitely a category on the post. What am I doing wrong?</p>