add a newline to /etc/machine-id as systemd does the same

mmdebstrap

@@ -3162,7 +3162,7 @@ sub run_cleanup() {
               or error "cannot unlink /etc/machine-id: $!";
             open my $fh, '>', "$options->{root}/etc/machine-id"
               or error "failed to open(): $!";
-            print $fh "uninitialized";
+            print $fh "uninitialized\n";
             close $fh;
         }
     }