Use absolute url's in opengraph tags, fixes #964

Author: Philippus

_includes/headertop.html

@@ -13,9 +13,9 @@
     <meta name="twitter:site" content="@scala_lang"/>
     <meta name="twitter:creator" content="@scala_lang"/>
     {% if page.url %}
-    <meta property="og:url" content="{{ site.baseurl }}{{ page.url }}"/>
+    <meta property="og:url" content="{{ site.url }}{{ page.url }}"/>
     {% endif %}    
-    <meta property="og:image" content="{{ site.baseurl }}/resources/img/scala-spiral-3d-2-toned-down.png"/>
+    <meta property="og:image" content="{{ site.url }}/resources/img/scala-spiral-3d-2-toned-down.png"/>
 
     <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
     <meta name="viewport" content="width=device-width, initial-scale=1"/>