gnome-terminal: load configuration at right time

If the dconf service hasn't been installed then the configuration
activation will fail. Thus, make sure the activation script is run after
packages have been installed.

modules/programs/gnome-terminal.nix

@@ -182,7 +182,8 @@ in
         sf = pkgs.writeText "gnome-terminal.ini" (toINI (buildIniSet cfg));
         dconfPath = "/org/gnome/terminal/legacy/";
       in
-        ''
+        # The dconf service needs to be installed and prepared.
+        stringAfter [ "installPackages" ] ''
           if [[ $DRY_RUN ]]; then
             echo ${pkgs.gnome3.dconf}/bin/dconf load ${dconfPath} "<" ${sf}
           else