Correct image link in meta tags

Author: pbinkley

_includes/head.html

@@ -6,7 +6,7 @@
   <meta name="description" content="{{ site.description }}">
   <link rel="stylesheet" href="{{ "/assets/bootstrap/css/bootstrap.min.css" | prepend: site.baseurl }}">
   <link rel="stylesheet" href="{{ "/css/main.css" | prepend: site.baseurl }}">
-  <link rel="canonical" href="{{ page.url | replace:'index.html','' | prepend: site.baseurl | prepend: site.url }}">
+  <link rel="canonical" href="{{ "assets/cover.jpg" | prepend: site.baseurl | prepend: site.url }}">
   <!-- HTML5 Shim and Respond.js IE8 support of HTML5 elements and media queries -->
   <!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
   <!--[if lt IE 9]>