fix for upcoming Pd-0.46 that has removed sched_tick() argument

in Pd-0.46, there is no more sys_time and sched_tick has it's argument removed
(as <<there's only one "reasonable" value to use anyhow>>").
Merge pull request #74 from umlaeute/schedtick_46

fix for upcoming Pd-0.46 that has removed sched_tick() argument