fix collectstats.pl cron for new Bugzilla

this was disabled in Ia76b4093d856f15a51218277f68e9b4540c4e2e6
because it caused cron spam

the difference is actually this:

on kaulen what it does was and is:

cd /srv/org/wikimedia/bugzilla/ ; ./collectstats.pl

when converting to module we changed that after a code review
comment to just be:

/srv/org/wikimedia/bugzilla/collectstats.pl

but with that you are getting :

Can't locate Bugzilla.pm in @INC

so, just do it like it has been done before and still works on kaulen

P.S. totally independent from this the script runs on kaulen
but reports some errors there when collecting the stats

Change-Id: I518a386c98bc0d30c682a6a57448fafb3ca4d33b