hplip_cron should do `export LANG=C' before command run

[Vladimir]

The `hplip_cron' script should do `export LANG=C' before to run any command. For example this line
    USAGE=`du -c $LOG_DIR 2>/dev/null |grep total |cut -d't' -f1`
will retuns nothing if LANG not C (my current locale is ru_RU.UTF8) and following
    while [ $USAGE -gt $MAXSIZE ]; do
will cause the error
    /etc/cron.daily/hplip_cron: line 17: [: -gt: ожидается использование унарного оператора
translation: unary operator expected.

My system:
Archlinux x86_64,
init:
  systemd,
/etc/locale.conf:
  LANG=ru_RU.UTF-8
  LC_COLLATE=C
  LOCALE=ru_RU.UTF-8