other: free backup ranges

Fix to memory leak I overlooked earlier.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

src/other.c

@@ -100,6 +100,7 @@ void clean_up(void)
 	free(config.output_file);
 	free(ranges);
 	free(leases);
+	free(backups);
 	free(touches);
 	free(shared_networks);
 }