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/misc/screen/default.nix

@@ -35,7 +35,7 @@ stdenv.mkDerivation rec {
   doCheck = true;
 
   meta = with stdenv.lib; {
-    homepage = http://www.gnu.org/software/screen/;
+    homepage = https://www.gnu.org/software/screen/;
     description = "A window manager that multiplexes a physical terminal";
     license = licenses.gpl2Plus;