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

@@ -2,7 +2,7 @@ Source: dns-flood-detector
 Section: net
 Priority: optional
 Maintainer: Jan Wagner <waja@cyconet.org>
-Build-Depends: debhelper-compat (= 12), libpcap0.8-dev
+Build-Depends: debhelper-compat (= 13), libpcap0.8-dev
 Homepage: http://www.adotout.com/
 Vcs-Browser: https://gitlab.uncompleted.org/debian/dns-flood-detector
 Vcs-Git: https://gitlab.uncompleted.org/debian/dns-flood-detector.git