HACKING: fix bad SVN repository URL

Change-Id: I593a4aec5495d874e60e5a380cceef50ec96f656
Reviewed-on: https://go-review.googlesource.com/c/163397
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/HACKING b/HACKING
index 8462d4e..fb48bb4 100644
--- a/HACKING
+++ b/HACKING
@@ -106,6 +106,6 @@
 
 For the convenience of people who want to use gccgo without waiting
 for a release and without living on tip, I maintain a gccgo branch of
-GCC.  This lives at svn://svn/gcc/branches/gccgo.  I maintain it using
-the general GCC branch policies described at
+GCC.  This lives at svn://gcc.gnu.org/svn/gcc/branches/gccgo.  I maintain
+it using the general GCC branch policies described at
 http://gcc.gnu.org/wiki/SvnBranch .