Fix hierarchy

Author: noamr

fetch.bs

@@ -8456,8 +8456,9 @@ otherwise false.
 </div>
 
 
-<h2 id=fetch-method>Fetch methods</h2>
+<h2 id="fetch-methods">Fetch methods</h2>
 
+<h3 id="fetch-method">Fetch Method</h3>
 <pre class=idl>
 partial interface mixin WindowOrWorkerGlobalScope {
   [NewObject] Promise&lt;Response> fetch(RequestInfo input, optional RequestInit init = {});