OSUpdateNotifier: ForceUpdateStartTimeInEpoch value set syntax

[phu-ngo]

code in line 970 need correct syntax
current:

# Determine the current start time in epoch seconds for forced update via GUI
ForceUpdateStartTimeInEpoch="$(/bin/date -jf "%a %b %d %T %Z %Y" "$(/bin/date)" +"%s")

Fix:

# Determine the current start time in epoch seconds for forced update via GUI
ForceUpdateStartTimeInEpoch="$(/bin/date +"%s")
```"