Treewide: use HTTPS on GNU domains

HTTP -> HTTPS for :
- http://gnu.org/
- http://www.gnu.org/
- http://elpa.gnu.org/
- http://lists.gnu.org/
- http://gcc.gnu.org/
- http://ftp.gnu.org/ (except in fetchurl mirrors)
- http://bugs.gnu.org/

pkgs/tools/text/diffutils/default.nix

@@ -21,7 +21,7 @@ stdenv.mkDerivation rec {
     ++ stdenv.lib.optional (stdenv.buildPlatform != stdenv.hostPlatform) "gl_cv_func_getopt_gnu=yes";
 
   meta = with stdenv.lib; {
-    homepage = http://www.gnu.org/software/diffutils/diffutils.html;
+    homepage = https://www.gnu.org/software/diffutils/diffutils.html;
     description = "Commands for showing the differences between files (diff, cmp, etc.)";
     license = licenses.gpl3;
     platforms = platforms.unix;