doc: fix header depth of util.isSymbol

jasnell · Myles Borins · commit 0013af61de0c · 2016-07-14T12:44:47.000-07:00
PR-URL: #7138 Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Anna Henningsen <anna@addaleax.net>
diff --git a/doc/api/util.md b/doc/api/util.md
@@ -498,7 +498,7 @@ util.isString(5)
   // false
 ```
 
-## util.isSymbol(object)
+### util.isSymbol(object)
 
     Stability: 0 - Deprecated
 
