Ubuntu 18 not generating files when maxEntriesPerFile is set or sitemap_parts with more than 50000 urls

[windson]

Do you want to request a feature or report a bug?
bug
What is the current behavior?
On windows when maxEntriesPerFile is set the behavior works as expected by generating sitemap_parts{}.xml and a consolidated sitemap.xml. But the same configuration doesn't works on Ubuntu 18. But I could see the part files in /tmp directory with sitemap_somehash of ubuntu os. Its just that the process is not able to generate the consolidated xml and part xmls.

If you provide a small website with 50 urls without maxEntriesPerFile, it works as expected on both Ubuntu 18 and Windows 10.
If the current behavior is a bug, please provide the steps to reproduce.

const SitemapGenerator = require('sitemap-generator');

const site = 'ifsc.icalci'
// create generator
const generator = SitemapGenerator('https://www.example.com', {
  stripQuerystring: false,
  maxDepth: 0,
  filepath: './sitemap.xml',
  priorityMap: [1.0, 0.9],
  maxEntriesPerFile: 12, // if not provided for large files with more than 50000 urls, then also it behaves as reported.
  timeout: 5000,
  maxConcurrency: 7,
  userAgent: 'Node/SitemapGenerator',
  lastMod: true,
  changeFreq: 'monthly'
});
// https://github.com/lgraubner/sitemap-generator/pull/76
let cnt = 0;
console.time(site)
generator.on('add', (url) => {
    cnt++;
    //console.log(url)
    if (cnt % 500 == 0)
    {
        console.log("added " + cnt.toString() + " urls")
    }
});

generator.on('error', (error) => {
    console.log(error);
    console.log("Failed at " + cnt.toString() + " processing URL :'( ")
});


// register event listeners
generator.on('done', () => {
  // sitemaps created
  console.log("Done adding " + cnt.toString() + " Urls successfully ��")
  console.timeEnd(site)
});

// start the crawler
generator.start();

What is the expected behavior?

Should be able to generate parts sitemap along with mapping sitemap.xml on Ubuntu 18