html: remove G+ reference from testdata

A bot inside Google was nagging me about this so change plusone to
minusone to hide it from the bot which doesn't understand that it's
just test data.

Change-Id: I2300a3e8c2ca969d61cae2d6bdc0683743b534e1
Reviewed-on: https://go-review.googlesource.com/c/162888
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>

html/testdata/go1.html

@@ -37,7 +37,7 @@ _gaq.push(["_trackPageview"]);
 <div id="page" class="wide">
 
 
-  <div id="plusone"><g:plusone size="small" annotation="none"></g:plusone></div>
+  <div id="minusone"><g:minusone size="small" annotation="none"></g:minusone></div>
   <h1>Go 1 Release Notes</h1>
 
 
@@ -2229,7 +2229,7 @@ after a few more words <a href="/LINK">link text</a>.<br>
 <script type="text/javascript">
   (function() {
     var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true;
-    po.src = 'https://apis.google.com/js/plusone.js';
+    po.src = 'https://apis.google.com/js/minusone.js';
     var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s);
   })();
 </script>