Shorten the duration needed in preemptive::test::does_not_predict_old_ports.
This patch shortens the duration of the does_not_predict_old_ports
test in the preemptive module. AppVeyor spawns its VMs/containers per
build, so the Instant::now()
call returns a value smaller than 60 * 60 + 1
which causes the subtraction to overflow and thus panic.
Thanks to @trinity-1686a for the help here.
See: #563 (closed).