fix heading for semantics

layouts/article/single.html

@@ -4,9 +4,9 @@
 
   <article class="center cf pv5 measure-wide-l">
 
-    <h4 class="f6">
+    <p class="f6 fw8">
       {{ humanize .Section | upper  }}
-    </h4>
+    </p>
     <h1>
       {{ .Title }}
     </h1>