doc: fix broken link to RTEMS Go wiki page

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/98740046

doc/gccgo_install.html

@@ -522,4 +522,4 @@ port is for x86. The goal is to extend the port to most of the
 <a href="http://www.rtems.org/wiki/index.php/SupportedCPUs">
 architectures supported by <code>RTEMS</code></a>. For more information on the port,
 as well as instructions on how to install it, please see this
-<a href="http://www.rtems.com/wiki/index.php/GCCGoRTEMS"><code>RTEMS</code> Wiki page</a>.
+<a href="http://www.rtems.org/wiki/index.php/GCCGoRTEMS"><code>RTEMS</code> Wiki page</a>.