title: Can't add class on select form helper in Rails 4
body: <p>Using Rails 4. Can't seem to add <code>class</code> to <code>select</code>. I think other attributes like <code>required</code>, <code>autofocus</code> are also not there:</p>
  
  <pre><code>&lt;%= form.select "availability", options_for_select(1..200), required: 'true', autofocus: 'true', class: 'form-control' %&gt;
  </code></pre>
  
  <p>Output is below:</p>
  
  <pre><code>&lt;select id="event_availability" name="event[availability]"&gt;
    &lt;option value="1"&gt;1&lt;/option&gt;
    &lt;option value="2"&gt;2&lt;/option&gt;
    &lt;option value="3"&gt;3&lt;/option&gt;
    ...
  &lt;/select&gt;
  </code></pre>
  
  <p>Any idea? Thanks.</p>