update/update_processes.cf: use sys.bindir only on 3.6 or newer

(cherry picked from commit 67360f8f87c3c5c7f1a4909e3527be6d52739449)
Merge pull request #213 from tzz/bindir-fixes-3.6.x

update/update_processes.cf: use sys.bindir only on 3.6 or newer