fix: Assume GB when no unit is present (#562)

  [ -z "$DISK_SPACE" ] && DISK_SPACE="16G"

  DISK_SPACE=$(echo "${DISK_SPACE^^}" | sed 's/MB/M/g;s/GB/G/g;s/TB/T/g')

  [[ -z "${DISK_SPACE//[0-9]}" ]] && DISK_SPACE="${DISK_SPACE}G"

  DATA_SIZE=$(numfmt --from=iec "$DISK_SPACE")

  if (( DATA_SIZE < 1 )); then

      error "Invalid value for ${DISK_DESC^^}_SIZE: $DISK_SPACE" && exit 73

  fi

  if (( DATA_SIZE < 104857600 )); then

    error "Please increase ${DISK_DESC^^}_SIZE to at least 100 MB." && exit 73

  fi

  FS=$(stat -f -c %T "$DIR")

  checkFS "$FS" "$DISK_FILE" "$DISK_DESC" || exit $?