title: Rails link_to with font-awesome and external url
body: <p>I'm trying to link to a youtube page in a rails app with the font-awesome gem. </p>
  
  <pre><code>&lt;i&gt;&lt;%= link_to fa_icon "youtube-square 2x", @book.youtube %&gt;&lt;/i&gt;
  </code></pre>
  
  <p>In doing so, I receive <code>no implicit conversion of Symbol into String</code> error message.  </p>
  
  <p>Do I need to remove the font-awesome helper and include it as a class, or is there another way to make this work together?</p>