Bump debhelper from deprecated 9 to 12.

Changes-By: lintian-brush
Fixes: lintian: package-uses-deprecated-debhelper-compat-version
See-also: https://lintian.debian.org/tags/package-uses-deprecated-debhelper-compat-version.html

debian/compat

-9
+12

debian/control

 Source: systemd-docker
 Priority: optional
 Maintainer: ale <ale@incal.net>
-Build-Depends: debhelper (>=9), dh-golang, golang-any (>=1.11)
+Build-Depends: debhelper (>= 12~), dh-golang, golang-any (>= 1.11)
 Standards-Version: 3.9.6
 
 Package: systemd-docker