title: Activeadmin and Formtastic: form not responding to :size
body: <p>I am trying to format a form and the text fields respond to some methods, and not others.</p>
  
  <p>I can do things like:</p>
  
  <pre><code>f.input :name, :input_html =&gt; { :maxlength =&gt; 10 }
  f.input :name, :input_html =&gt; { :disabled =&gt; true }
  </code></pre>
  
  <p>But if I try to do any of the following, they do not work:</p>
  
  <pre><code>f.input :name, :input_html =&gt; { :size =&gt; 10 }
  f.input :name, :input_html =&gt; { :class =&gt; 'autogrow' }
  f.input :name, :input_html =&gt; { :rows =&gt; 10, :cols =&gt; 10 }
  </code></pre>
  
  <p>When I try using :size, for instance, the generated html shows that size=10, but is not reflected in the actual form.</p>
  
  <p>These were more or less pulled right from the Formtastic documentation on Github, which the Activeadmin documentation refers to.</p>