How to use the puppeteer._launcher function in puppeteer

function phantomas(url, opts) {
	var events = new EventEmitter(),
		browser, options;

	debug('OS: %s %s', process.platform, process.arch);
	debug('Node.js: %s', process.version);
	debug('phantomas: %s', VERSION);
	debug('Puppeteer: preferred revision r%s', puppeteer._launcher._preferredRevision);
	debug('URL: <%s>', url);

	// options handling
	options = util._extend({}, opts || {}); // use util._extend to avoid #563
	options.url = options.url || url || false;

	debug('Options: %s', JSON.stringify(options));

	events.setMaxListeners(100); // MaxListenersExceededWarning: Possible EventEmitter memory leak detected.

	var results = new Results();
	results.setUrl(url);
	results.setGenerator('phantomas v' + VERSION);

	// set up and run Puppeteer
	browser = new Browser();