doc: fix release notes anchor tag

R=r, r2
CC=golang-dev
https://golang.org/cl/4178055

doc/devel/release.html

@@ -5,7 +5,7 @@
 <p>This page summarizes the changes between tagged releases of Go.
 For full details, see the <a href="http://code.google.com/p/go/source/list">Mercurial change log</a>.</p>
 
-<h3 id="2011-02-01">2011-02-15</h3>
+<h3 id="2011-02-15">2011-02-15</h3>
 
 <pre>
 This release includes changes to the io and template packages.