Add type for favicon

layouts/partials/head.html

 
   <!-- Icons -->
   <link rel="apple-touch-icon-precomposed" sizes="144x144" href="/apple-touch-icon-144-precomposed.png">
-  <link rel="shortcut icon" href="/favicon.png">
+  <link rel="shortcut icon" type="image/png" href="/favicon.png">
 
   <!-- RSS -->
   <link href="{{ .RSSLink }}" rel="alternate" type="application/rss+xml" title="{{ .Site.Title }}" />