title: perform a where in query in bookshelf.js
body: <p>I want to perform a <code>WHERE - IN</code> query/operation but normal where gives error.</p>
  
  <p>I want this</p>
  
  <pre><code>select * from `calendar_event_rsvp` where `event_id` in ('1', '2', '3')
  </code></pre>
  
  <p>But below code leads to </p>
  
  <pre><code>select * from `calendar_event_rsvp` where `event_id in` = '1', '2', '3'
  </code></pre>
  
  <p><strong>Code</strong></p>
  
  <pre><code>CalendarEventRSVP.forge()
                  .where({
                      "event_id": event_ids
                  })
  </code></pre>
  
  <p>How do i do this in bookshelf.js </p>