fixes #327 specify xz compression for deb files explicitly

It seems that the new default since deb 1.19/Ubuntu 21.10 is zst, which is not yet supported everywhere.

build.gradle

@@ -194,7 +194,7 @@ def deb(def platform, def arch, def moreDeps = '') {
         ant.arg(line: "a+x usr/bin/ipscan usr/lib/ipscan/${project.name}-${platform}-${version}.jar")
     }
     ant.exec(executable: 'fakeroot', dir: dist + '/..', failonerror: true) {
-        ant.arg(line: "dpkg-deb -b deb ${project.name}_${version}_${arch}.deb")
+        ant.arg(line: "dpkg-deb -Zxz -b deb ${project.name}_${version}_${arch}.deb")
     }
     ant.delete(dir: dist)
 }