Update feed.xml

Author: tuanductran

feed.xml

@@ -17,7 +17,7 @@ layout: null
         <description>{{ post.content | xml_escape }}</description>
         <pubDate>{{ post.date | date_to_rfc822 }}</pubDate>
         <link>{{ site.url }}{{ post.url }}</link>
-        <guid isPermaLink="true">{{ site.url }{{ post.url }}</guid>
+        <guid isPermaLink="true">{{ site.url }}{{ post.url }}</guid>
         {% for tag in post.tags %}
         <category>{{ tag | xml_escape }}</category>
         {% endfor %}