ack-sel command is formatted incorrectly

The ack-sel action has a formatting error that causes it to quietly fail.

When using the action, a typical output looks like:
```
$ juju run-action hw-health/669 ack-sel --wait
unit-hw-health-669:
  UnitId: hw-health/669
  id: "141747"
  results:
    message: Only SEL entries newer than 2021-06-28 will be considered
  status: completed
  timing:
    completed: 2021-06-28 21:38:17 +0000 UTC
    enqueued: 2021-06-28 21:38:17 +0000 UTC
    started: 2021-06-28 21:38:17 +0000 UTC
```

Which seems to indicate success. However, Thruk catches that this action exits with code 1:
```
UNKNOWN: invalid sensor type '--date-range=06/28/2021-now'

-> Execution of /usr/sbin/ipmi-sel failed with return code 1.
-> /usr/sbin/ipmi-sel was executed with the following parameters:
sudo /usr/sbin/ipmi-sel --output-event-state --interpret-oem-data --entity-sensor-names --sensor-types=all --exclude-sensor-types=battery,entity_presence,module_board --exclude-sensor-types=Management_Subsystem_Health --date-range=06/28/2021-now
```

Manually running the above command works. Looking at it, the formatting is correct and there is no reason for --date-range to be mistaken as part of --exclude-sensor-types.

However, when looking at /etc/cron.d/hwhealth_ipmi, I find an error:
```
/etc/cron.d$ cat hwhealth_ipmi
3,8,13,18,23,28,33,38,43,48,53,58 * * * * nagios /usr/local/lib/nagios/plugins/cron_ipmi_sensors.py -xT battery,entity_presence,module_board -xST battery,entity_presence,module_board --seloptions --exclude-sensor-types=Management_Subsystem_Health,--date-range=06/28/2021-now --sexclude /var/lib/nagios/ipmi_exclude
```

Here we can see that a space between --exclude-sensor-types and --date-range is been replaced with a comma. If I manually correct this file then run the action again, the formatting mistake is restored.

I've replicated this behavior on a second hw-health unit running on a different host.