fix missing underscore

_layouts/page.html

@@ -4,6 +4,6 @@ layout: default
 
 <h1 id="title-heading" class="page-title">{{ page.title }}</h1>
 
-{% include page_toc.html html=content hmax=3 %}
+{% include page_toc.html html=content h_max=3 %}
 
 {{ content }}