dir: Fix grammar in an error message
dir: Fix grammar in an error message

flatpak/flatpak,flatpak/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak