Update HtmlHelper.php

Error favicon: line 279: $options['link'] = $this->assetUrl($options['link']);

error html:
<link href="/cakephp-posts/cakephp-posts/favicon.ico" type="image/x-icon" rel="icon" />

 to

<link href="/cakephp-posts/favicon.ico" type="image/x-icon" rel="icon" />