fix search meta tag.

_layouts/base.html

@@ -7,7 +7,8 @@
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <meta http-equiv="last-modified" content="{{ site.time }}">
     <meta name="viewport" content="width=device-width, initial-scale=1">
-    <meta name="search-domain" value="{{ page.root }}">
+    <!-- meta "search-domain" used for google site search function google_search() -->
+    <meta name="search-domain" value="{{ site.github.url }}">
     <link rel="stylesheet" type="text/css" href="{{ page.root }}/assets/css/bootstrap.css" />
     <link rel="stylesheet" type="text/css" href="{{ page.root }}/assets/css/bootstrap-theme.css" />
     <link rel="stylesheet" type="text/css" href="{{ page.root }}/assets/css/lesson.css" />