Fix duplicated environment values

All profileVariables listed each profile twice (e.g. $PATH contained
$HOME/.nix-profile/bin twice).  This is because mergeAttrsWithFunc is
broken (and deprecated):

  nix-repl> :p mergeAttrsWithFunc concat { x = [1]; } { y = [2]; }
  { x = [ 1 ]; y = [ 2 2 ]; }

So use zipAttrsWith instead.

modules/config/shells-environment.nix

@@ -154,7 +154,7 @@ in
          ${concatStringsSep "\n" (
            (mapAttrsToList (n: v: ''export ${n}="${concatStringsSep ":" v}"'')
              # This line is a kind of a hack because of !!! note above
-             (fold (mergeAttrsWithFunc concat) {} ([ (mapAttrs (n: v: [ v ]) cfg.variables) ] ++ map cfg.profileVariables cfg.profiles))))}
+             (zipAttrsWith (const concatLists) ([ (mapAttrs (n: v: [ v ]) cfg.variables) ] ++ map cfg.profileVariables cfg.profiles))))}
 
          ${cfg.extraInit}