Use assets and meta tags for og tags

Author: palewire

_includes/head.html

@@ -8,8 +8,8 @@
     <title>{{ site.title }} {% if page.title %}| {{ page.title }}{% endif %}</title>
     <meta property="og:title" content="Project Jupyter" />
     <meta property="og:description" content="{{ site.description }}">
-    <meta property="og:url" content="https://www.jupyter.org" />
-    <meta property="og:image" content="https://jupyter.org/assets/homepage.png" />
+    <meta property="og:url" content="{{ site.url }}" />
+    <meta property="og:image" content="{{ "/assets/homepage.png" | prepend: site.url }}" />
     <link rel="canonical" href="{{ page.url | prepend: site.url }}">
     <!-- Bootstrap Core CSS -->
     <link rel="stylesheet" href="{{ "/css/bootstrap.min.css" | prepend: site.baseurl }}">