doc: add Go 1.2 to release history page

Fixes #6939.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/41540043

doc/devel/release.html

@@ -13,12 +13,19 @@ hg pull
 hg update <i>tag</i>
 </pre>
 
+<h2 id="go1.2">go1.2 (released 2013/12/01)</h2>
+
+<p>
+Go 1.2 is a major release of Go.
+Read the <a href="/doc/go1.2">Go 1.2 Release Notes</a> for more information.
+</p>
+
+
 <h2 id="go1.1">go1.1 (released 2013/05/13)</h2>
 
 <p>
 Go 1.1 is a major release of Go.
-Read the <a href="/doc/go1.1.html">Go 1.1 Release Notes</a> for
-more information.
+Read the <a href="/doc/go1.1">Go 1.1 Release Notes</a> for more information.
 </p>
 
 <h3 id="go1.1.minor">Minor revisions</h3>