[css-nav-1] Fix the mistake in processing model

If the best candidate is found, "navbeforefocus" event should be fired. (not "navnotarget")

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -1070,7 +1070,7 @@ To run the <dfn>spatial navigation steps</dfn> in <var>direction</var>, do the f
     </ul>
 8. Let <var>bestCandidate</var> be the result of <a>selecting the best candidate</a>
     within <var>candidates</var> in <var>direction</var> starting from <var>eventTarget</var>.
-9. <a>Dispatches navnotarget event</a> at <var>eventTarget</var> with <var>direction</var> and <var>bestCandidate</var>.
+9. <a>Dispatches navbeforefocus event</a> at <var>eventTarget</var> with <var>direction</var> and <var>bestCandidate</var>.
 10. Run the <a>focusing steps</a> for <var>bestCandidate</var> and return.
 
 </div>