Update source/_includes/custom/header.html

fix header link

Author: gyteng

source/_includes/custom/header.html

@@ -1,6 +1,6 @@
 <hgroup>
-  <h1><a href="{{ root_url }}/">{{ site.title }}</a></h1>
+  <h1>{{ site.subtitle }}</h1>
   {% if site.subtitle %}
-    <h2>{{ site.subtitle }}</h2>
+    <h2><a href="{{ root_url }}/">{{ site.title }}</a></h2>
   {% endif %}
 </hgroup>