HACKING: update links to use https://

Change-Id: I73e715eb272d45f1facdea62b5eeb47cf801477e
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/239937
Reviewed-by: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/HACKING b/HACKING
index 6ab5371..f6e5dd9 100644
@@ -20,10 +20,10 @@
 git clone https://go.googlesource.com/gofrontend
-(or use the mirror on github: git clone http://github.com/golang/gofrontend)
+(or use the mirror on github: git clone https://github.com/golang/gofrontend)
 That gives you the frontend only.  Now you need a copy of the GCC
-source code.  See http://gcc.gnu.org/git.html for details, or simply:
+source code.  See https://gcc.gnu.org/git.html for details, or simply:
 git clone git://gcc.gnu.org/git/gcc
@@ -47,7 +47,7 @@
 This is all you need to build gccgo yourself and develop your own
 patches.  To get your patch committed, send them in using "git
 codereview mail" as described at
-http://golang.org/doc/gccgo_contribute.html ; it's the same process as
+https://golang.org/doc/gccgo_contribute.html ; it's the same process as
 changes for the regular Go repository.
 At present I am the only person who commits changes to the Go frontend
@@ -108,4 +108,4 @@
 for a release and without living on tip, I maintain a gccgo branch of
 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 .
+https://gcc.gnu.org/wiki/SvnBranch .