update_all's update hash doesn't have any magic performed on bare Time
objects; it assumes any Time object it's given is already in UTC. using
a TimeWithZone object (regardless of timezone), which Fixnum#ago and
friends happen to return, is still fine.
Change-Id: I297b2a3211b896b5225ebcfaaee3c1eb56e55fb6
Reviewed-on: https://gerrit.instructure.com/5351
Tested-by: Hudson <hudson@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>