title: failure to get fbOAuth in Rfacebook
body: <p>I would like to get fbOAuth to access live-long access token using packages <code>Rfacebook</code></p>
  
  <p>I got <code>app_id</code> and <code>app_secret</code> from <a href="https://developers.facebook.com/apps," rel="nofollow">this link</a> after registrated an app. <br>
  It required me to <code>"Copy and paste into Site URL on Facebook App Settings: http://localhost:1410/"</code></p>
  
  <p>I am not sure where i should paste the link to. And got error when</p>
  
  <pre><code>&gt; fb_oauth &lt;- fbOAuth(app_id, app_secret, extended_permissions = TRUE) 
  Copy and paste into Site URL on Facebook App Settings: http://localhost:1410/ 
  When done, press any key to continue...
  Error in authorizer(authorize_url) : 
    httpuv package required to capture OAuth credentials.
  </code></pre>
  
  <p>Thanks.</p>