fixed favicon's MIME type (#915)

Author: Daniel Bushman

themes/vue/layout/layout.ejs

@@ -17,7 +17,7 @@
         <meta name="twitter:description" content="<%- theme.site_description %>">
         <meta name="twitter:image" content="https://<%- theme.root_domain %>/images/logo.png">
 
-        <link rel="icon" href="<%- url_for("/images/logo.png") %>" type="image/x-icon">
+        <link rel="icon" href="<%- url_for("/images/logo.png") %>" type="image/png">
 
         <link href='//fonts.googleapis.com/css?family=Source+Sans+Pro:300,400,600|Roboto Mono' rel='stylesheet' type='text/css'>
         <link href='//fonts.googleapis.com/css?family=Dosis:500&text=Vue.js' rel='stylesheet' type='text/css'>