don't include unpublished in feed

feed.xml

@@ -12,6 +12,9 @@ layout: null
     <lastBuildDate>{{ site.time | date_to_rfc822 }}</lastBuildDate>
     <generator>Jekyll v{{ jekyll.version }}</generator>
     {% for post in site.posts limit:10 %}
+      {% if post.published == false %}
+        {% continue %}
+      {% endif %}
       <item>
         <title>{{ post.title | xml_escape }}</title>
         <description>{{ post.content | xml_escape }}</description>