doc/go1.3.html: fix id anchor for FreeBSD

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/88000047

doc/go1.3.html

@@ -53,7 +53,7 @@ as of Go 1.3 it is not supported by Go either.
 </p>
 
 
-<h3 id="solaris">Support for FreeBSD</h3>
+<h3 id="freebsd">Support for FreeBSD</h3>
 
 <p>
 It was not announced at the time, but since the release of Go 1.2, support for Go on FreeBSD