doc/devel/release.html: fix dumb typo

R=r
CC=golang-dev
https://golang.org/cl/186148

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="2010-01-13">2010-01-13</h2>
+<h3 id="2010-01-13">2010-01-13</h3>
 
 <pre>
 build: $GOBIN should no longer be required in $PATH (thanks Devon H. O'Dell),