Log Message:
s6: update to 2.13.1.0. Changes:

- Bugfixes.
- s6-supervise now supports a new file in the service directory:
  flag-newpidns. If this file is present at service spawning time, the
  process will be started in a new PID namespace. (Linux only; on other
  systems, the service will fail to start if the file exists.)