playground: s/it/this/

R=r, r2
CC=golang-dev
https://golang.org/cl/2663041

doc/root.html

@@ -51,7 +51,7 @@ google.setOnLoadCallback(loadFeed);
       </p>
       <h2>Check it out!</h2>
       <p>
-      <div class="how">[<a href="/doc/playground.html">How does it work?</a>]</div>
+      <div class="how">[<a href="/doc/playground.html">How does this work?</a>]</div>
       <a href="/doc/install.html">Install Go now</a>, or try it right here in your browser:</p>
       <div id="playground" class="small"></div>
       <script src="/doc/play/playground.js"></script>