bug fix

examples/tunasync.conf

@@ -15,6 +15,7 @@ ctrl_addr = "/tmp/tunasync.sock"
 [btrfs]
 service_dir = "{mirror_root}/_current/{mirror_name}"
 working_dir = "{mirror_root}/_working/{mirror_name}"
+gc_root = "{mirror_root}/_garbage/"
 gc_dir = "{mirror_root}/_garbage/_gc_{mirror_name}_{{timestamp}}"
 
 # [[mirrors]]