Fix key event used for close requests

Esc keydown has always been what triggered close request behavior. This was just a mistake in writing the spec.

Author: domenic

source

@@ -81760,7 +81760,7 @@ body { display:none }
    is <span>implementation-defined</span>, except that if <code
    data-x="event-keydown">keydown</code> and <code data-x="event-keyup">keyup</code> events were
    fired for the <kbd>Esc</kbd> key, the user agent must pick the <code
-   data-x="event-keyup">keyup</code> event.</p></li>
+   data-x="event-keydown">keydown</code> event.</p></li>
 
    <li><p>If <var>event</var> is not null, and its <span>canceled flag</span> is set, then
    return.</p></li>