append extend 8 to android code version.

append_8_to_version_code.js

#!/usr/bin/env node

var path = require('path');
var fs = require('fs');
var xml2js = require('xml2js');

function xmlFileToJs(filename, cb) {
    var filepath = path.normalize(path.join(__dirname, filename));
    fs.readFile(filepath, 'utf8', function (err, xmlStr) {
        if (err) throw (err);
        xml2js.parseString(xmlStr, {}, cb);
    });
}

function jsToXmlFile(filename, obj, cb) {
    var filepath = path.normalize(path.join(__dirname, filename));
    var builder = new xml2js.Builder();
    var xml = builder.buildObject(obj);
    fs.writeFile(filepath, xml, cb);
}

var androidManifestRPath = '../../platforms/android/AndroidManifest.xml';
xmlFileToJs(androidManifestRPath, function(error, data) {
  var config = data;
  config.manifest.$['android:versionCode'] += '8';
  jsToXmlFile(androidManifestRPath, config)
});

This code not running with Cordova 9.0, error:

Error: Callback must be a function. Received undefined

Use this: https://gist.github.com/ricardoapaes/66f07c0a46c3e7dadf488aa66b93fff7