Bump debhelper from old 12 to 13.

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

debian/control

@@ -3,7 +3,7 @@ Section: ruby
 Priority: optional
 Maintainer: Debian Ruby Team <pkg-ruby-extras-maintainers@lists.alioth.debian.org>
 Uploaders: Sebastien Badia <sbadia@debian.org>
-Build-Depends: debhelper-compat (= 12), gem2deb, rake, ruby-rspec
+Build-Depends: debhelper-compat (= 13), gem2deb, rake, ruby-rspec
 Standards-Version: 4.1.3
 Vcs-Git: https://salsa.debian.org/ruby-team/ruby-powerpack.git
 Vcs-Browser: https://salsa.debian.org/ruby-team/ruby-powerpack