gulp clean为何无法删除文件夹?

gulp.task('clean', function() { fs.rmdir('tmp', function(){ console.info('remove file .'); }); fs.rmdir('tmp2', function(){ console.info('remove file ..'); }); });

	[08:02:06] Starting 'cleanx'...
	[08:02:06] Finished 'cleanx' after 898 μs
	remove file .
	remove file ..
	

看了下,文件夹还在,怎么回事?