stuartmls

Fix ps check of child pids on BSD-based MacOS. Use pgrep instead.

2

Issue: Unregistering a service results in the following error: ``` ps: illegal option -- - usage: ps [-AaCcEefhjlMmrSTvwXx] [-O fmt | -o fmt] [-G gid[,gid...]] [-g grp[,grp...]] [-u [uid,uid...]] [-p...