fix header nav highlight

site/templates/layout.html

@@ -95,7 +95,7 @@
           <li class="{%- if post.directory|rootDirectoryIs('docs') %}current{%- endif %}">
             <a href="/docs/introduce">使用</a>
           </li>
-          <li class="{%- if post.directory|rootDirectoryIs('design') %}current{%- endif %}">
+          <li class="{%- if post.directory|rootDirectoryIs('spec') %}current{%- endif %}">
             <a href="/spec/font">设计</a>
           </li>
           <li class="{%- if post.directory|rootDirectoryIs('components') %}current{%- endif %}">