Unzip xls should use buffer instead of string

[yujiang]

Unzip xlsx should use buffer instead of string , or there will be error when unzip large chinese xlsx

function extractFiles(path, sheet) {
...
.on('entry', function (entry) {
var file = files[entry.path];
if (file) {
//let contents = '';
let buffer = new Buffer("");
filePromises.push(new Promise((resolve) => {
entry
//.on('data', data => contents += data.toString())
.on('data', (data) => {
buffer = Buffer.concat([buffer,data])
})
.on('end', () => {
//files[file].contents = contents;
files[file].contents = buffer.toString();
resolve();
});
}));
} else {
entry.autodrain();
}
});
...