Update debhelper compat to 12

debian/changelog

 dkimpy-milter (1.2.2-1) unstable; urgency=medium
 
   * New upstream release
+  * Update debhelper compat to 12
 
  -- Scott Kitterman <scott@kitterman.com>  Sun, 09 Aug 2020 15:26:51 -0400
 

debian/control

@@ -3,7 +3,7 @@ Section: mail
 Priority: optional
 Maintainer: Scott Kitterman <scott@kitterman.com>
 Uploaders: Python Applications Packaging Team <python-apps-team@lists.alioth.debian.org>
-Build-Depends: debhelper-compat (= 11),
+Build-Depends: debhelper-compat (= 12),
                dh-python,
                python3 (>= 3.3),
                python3-authres (>= 1.1),