docs: Switch to the asynchronous Google Analytics snippet

The old snippet needlessly uses `document.write`. Let’s use the
optimized version of the most recent, asynchronous GA snippet:
http://mathiasbynens.be/notes/async-analytics-snippet

doc/template.html

@@ -66,21 +66,20 @@
             <li><a href="http://twitter.com/nodejs" class="twitter">@nodejs</a></li>
         </ul>
 
-        <p>Copyright <a href="http://joyent.com">Joyent, Inc</a>, Node.js is a <a href="/trademark-policy.pdf">trademark</a> of Joyent, Inc. View <a href="https://raw.github.com/joyent/node/__VERSION__/LICENSE">license</a>.</p>
+        <p>Copyright <a href="http://joyent.com/">Joyent, Inc</a>, Node.js is a <a href="/trademark-policy.pdf">trademark</a> of Joyent, Inc. View <a href="https://raw.github.com/joyent/node/__VERSION__/LICENSE">license</a>.</p>
     </div>
 
   <script src="../sh_main.js"></script>
   <script src="../sh_javascript.min.js"></script>
   <script>highlight(undefined, undefined, 'pre');</script>
   <script>
-    var gaJsHost = (("https:" == document.location.protocol) ?
-    "https://ssl." : "http://www.");
-    document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));
+    window._gaq = [['_setAccount', 'UA-10874194-2'], ['_trackPageview']];
+    (function(d, t) {
+      var g = d.createElement(t),
+          s = d.getElementsByTagName(t)[0];
+      g.src = '//www.google-analytics.com/ga.js';
+      s.parentNode.insertBefore(g, s);
+    }(document, 'script'));
   </script>
-  <script>
-    try {
-      var pageTracker = _gat._getTracker("UA-10874194-2");
-      pageTracker._trackPageview();
-      } catch(err) {}</script>
 </body>
 </html>