title: how to query builder select inside select on laravel
body: <p>I have some trouble with Laravel Query Builder. I want to convert this SQL Query:</p>
  
  <pre><code>select (select sum(amount) from transactions t
              join sale w on w.id = t.sale_id
              join types s on s.id = w.type_id
              where s.name = 'Bronze'
          ) as sum_amount
      from transactions
      limit 1;
  </code></pre>
  
  <p>How to implement this query on my laravel query builder ?
  I'm using laravel 5.2</p>
  
  <p>hope someone help me :) thanks</p>