[mediaqueries] Make both parts of the example reference 'speech'.

Author: tabatkins

mediaqueries/Overview.bs

@@ -729,7 +729,7 @@ Error Handling</h3>
 	<div class='example'>
 		<pre>
 			@media (example, all,), speech { /* only applicable to speech devices */ }
-			@media &test, screen           { /* only applicable to screen devices */ }
+			@media &test, speech           { /* only applicable to speech devices */ }
 		</pre>
 
 		Both of the above <a>media query lists</a> are turned into ''not all, speech'' during parsing,