Bugfix with logrotate

Changing rights to avoid this issue with logrotate:

/etc/cron.daily/logrotate:
error: skipping "/var/log/lshell/lshell.log" because parent directory
has insecure permissions (It's world writable or writable by group which
is not "root") Set "su" directive in config file to tell logrotate which
user/group should be used for rotation.