Pre-Depends: init-system-helpers

[Bastien ROUCARIES <roucaries.bastien@gmail.com>]

Hi,

In order to solve #769551 I need to Pre-Depends: init-system-helpers

Indeed preinst script need it:
/var/lib/dpkg/tmp.ci/preinst: 27: /var/lib/dpkg/tmp.ci/preinst:
deb-systemd-helper: not found

Thus I am asking to add a pre-depends to init-system-helpers