rubyGems.pg: fix postgresql path

Changed files
+1 -1
pkgs
development
ruby-modules
gem-config
+1 -1
pkgs/development/ruby-modules/gem-config/default.nix
···
pg = attrs: {
buildFlags = [
-
"--with-pg-config=${postgresql}/bin/pg_config"
];
};
···
pg = attrs: {
buildFlags = [
+
"--with-pg-config=${postgresql.dev}/bin/pg_config"
];
};