title: add :onchange => "readURL(this)" to input file on simple_form
body: <p>I have a problem with this:</p>
  
  <p>I want add  <code>:onchange =&gt; "readURL(this)"</code> to my:</p>
  
  <pre><code>&lt;%= f.input :image, :as =&gt; :file, :onchange =&gt; "readURL(this)" %&gt;
  </code></pre>
  
  <p>I have tried with:</p>
  
  <pre><code>&lt;%= f.input :image, :as =&gt; :file, :html =&gt; {:onchange =&gt;
  "readURL(this)"} %&gt;
  </code></pre>
  
  <p>but I can not see the  <code>onchange="readURL(this)"</code> in html code.</p>
  
  <p>How can I fix this problem?</p>
  
  <p>Thank you again :D. </p>