Use xz compression to restore Debian support

The default compression on deb packages seems to have changed to zstd.
Unfortunately, Debian does not support zstd (yet), so this specifies a friendlier format.

Fixes twilio#482

.github/scripts/pack-debian-apt.js

@@ -81,7 +81,7 @@ PATH=$PATH:$PWD/bin eval $(PATH=$PATH:$PWD/bin node -p "require('./package').scr
       await qq.chmod([workspace, 'usr/lib', config.dirname, 'bin', config.bin], 0o755);
       await qq.chmod([workspace, 'DEBIAN/postinst'], 0o755);
       await qq.x(`ln -s "../lib/${config.dirname}/bin/${config.bin}" "${workspace}/usr/bin/${pjson.oclif.bin}"`);
-      await qq.x(`dpkg --build "${workspace}" "${qq.join(dist, debArch(arch), `${versionedDebBase}.deb`)}"`);
+      await qq.x(`dpkg --build --compression=xz "${workspace}" "${qq.join(dist, debArch(arch), `${versionedDebBase}.deb`)}"`);
     }
     try {
       // fetch existing Packages file which needs to be modified for new version