added tags to header for articles. resolves #169

Author: davidwesst

src/_layouts/base.html

@@ -23,9 +23,12 @@
         <meta name="url" property="og:url" content="{{ page_url | url }}" />
         <meta name="description" property="og:description" content="{{ description }}" />
         {% if page_type == "article" %}
-        <meta name="author" property="article:author" content="{{ site.author }}" />
-        <meta name="published_time" property="article:published_time" content="{{ date }}" />
-        <meta name="publish_time" property="article:publish_date" content="{{ date }}" />
+        <meta name="author" property="og:article:author" content="{{ site.author }}" />
+        <meta name="published_time" property="og:article:published_time" content="{{ date }}" />
+        <meta name="publish_time" property="og:article:publish_date" content="{{ date }}" />
+        {% for tag in tags %}
+        <meta name="tag" property="og:article:tag" content="{{ tag }}" />
+        {% endfor %}
         {% endif %}
         {% if image %}
 		{% capture page_image %}