fix: zero number format bug

[ghost]

test demo in nodejs

var xlsx = require('node-xlsx');
var fs = require('fs');

const data = [[1, {t: 'n', f: 2, z: 2}, {t: 'n', f: 0, z: 2}]]

var buffer = xlsx.build([{name: "mySheetName", data: data}]); // Returns a buffer
fs.writeFileSync('test.xlsx', buffer)

before change

after change

[SheetJSDev]

The issue here is that f should be a string, not a number:

const data = [[1, {t: 'n', f: "2", z: 2}, {t: 'n', f: "0", z: 2}]]

So it's preferable to check if it is a string