Bump debhelper compat level to 11, adjust build-dependencies accordingly.

debian/compat

-10
+11

debian/control

@@ -3,7 +3,7 @@ Maintainer: Debian AppArmor Team <pkg-apparmor-team@lists.alioth.debian.org>
 Uploaders: intrigeri <intrigeri@debian.org>
 Section: admin
 Priority: optional
-Build-Depends: debhelper (>= 10),
+Build-Depends: debhelper (>= 11),
                dh-apparmor,
                apparmor (>= 2.9.0)
 Standards-Version: 4.1.1