Update homepage attributes: http -> https

Homepage link "http://.../" is a permanent redirect to "https://.../" and should be updated
https://repology.org/repository/nix_stable/problems

pkgs/development/libraries/gmp/4.3.2.nix

@@ -60,7 +60,7 @@ let self = stdenv.mkDerivation rec {
          asymptotically faster algorithms.
       '';
 
-    homepage = http://gmplib.org/;
+    homepage = https://gmplib.org/;
     license = stdenv.lib.licenses.lgpl3Plus;
 
     maintainers = [ ];