fix(site): absolute path to favicon (#3216)

I snuck this change in after initial approval. I hope it's small enough to not be considered scope creep.

Author: isaaccloos

_includes/head.html

@@ -11,8 +11,8 @@
 <script src="//html5shiv.googlecode.com/svn/trunk/html5.js"></script>
 <![endif]-->
 
-<link rel="shortcut icon" href="./icons/favicon.ico" type="image/x-icon">
-<link rel="icon" href="./icons/favicon.ico" type="image/x-icon">
+<link rel="shortcut icon" href="/icons/favicon.ico" type="image/x-icon">
+<link rel="icon" href="/icons/favicon.ico" type="image/x-icon">
 
 <link rel="canonical" href="{{ page.url | replace:'index.html','' | prepend: site.baseurl | prepend: site.url }}">