in gulpfile.js [137:145]
function jekyllBuild (done) {
const bundle = getBundleExecutable();
const configs = getJekyllConfigs();
let flags = argv.prod ? PROD_FLAGS : DEV_FLAGS;
flags = flags.concat(['--config', configs.join(',')]);
exec(bundle, ['exec', 'jekyll', 'build'].concat(flags), done);
}