Set debhelper-compat version in Build-Depends.

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

debian/compat

-12

debian/control

@@ -2,7 +2,7 @@ Source: apache-exporter
 Section: admin
 Priority: optional
 Maintainer: Autistici/Inventati <debian@autistici.org>
-Build-Depends: debhelper (>= 12~), golang-go, dh-golang
+Build-Depends: debhelper-compat (= 12), golang-go, dh-golang
 Standards-Version: 3.9.6
 
 Package: apache-exporter