godoc: switch on +1 buttons

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5754048

lib/godoc/godoc.html

@@ -61,7 +61,6 @@ Creative Commons Attribution 3.0 License.
 </div>
 
 </body>
-<!--
 <script type="text/javascript">
   (function() {
     var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true;
@@ -69,6 +68,5 @@ Creative Commons Attribution 3.0 License.
     var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s);
   })();
 </script>
--->
 </html>