editorial: fix typo in browsingContext.downloadWillBegin anchor

Author: juliandescottes

index.bs

@@ -5438,7 +5438,7 @@ complete</dfn> steps given |navigable| and |navigation status|:
 
 </div>
 
-#### The browsingContext.downloadWillBegin Event #### {#event-browsingContext-downoadWillBegin}
+#### The browsingContext.downloadWillBegin Event #### {#event-browsingContext-downloadWillBegin}
 
 <dl>
    <dt>Event Type</dt>