treewide: update homepages to https where available

Based on "problems" from repology:

https://repology.org/repository/nix_unstable/problems

Mostly simple changes to reflect redirects.

pkgs/development/libraries/libmodbus/default.nix

@@ -20,7 +20,7 @@ stdenv.mkDerivation rec {
 
   meta = with stdenv.lib; {
     description = "Library to send/receive data according to the Modbus protocol";
-    homepage = http://libmodbus.org/;
+    homepage = https://libmodbus.org/;
     license = licenses.lgpl21Plus;
     platforms = platforms.linux;
     maintainers = [ maintainers.bjornfor ];