假设
check接受回调，我们可以使用它
mapSeries来实现。
async.mapSeries(files, function(file, outerCB) { var all = fs.readdirsync("./0"); async.mapSeries(all, function(item, cb){ check(item, cb); }, outerCB);}, function(err, results) { // This is called when everything's done});
