duplicated url are crawled twice

What is the current behavior?

Duplicated urls are not skipped. The same url is crawled twice.

If the current behavior is a bug, please provide the steps to reproduce

const HCCrawler = require('./lib/hccrawler');

(async () => {
  const crawler = await HCCrawler.launch({
    evaluatePage: () => ({
      title: document.title,
    }),
    onSuccess: (result => {
      /console.log(result);
    }),
    skipDuplicates: true,
    jQuery: false,
    maxDepth: 3,
    args: ['--no-sandbox']
  });
  
  await crawler.queue([{
        url: 'https://www.example.com/'
      }, {
        url: 'https://www.example.com/'
  }]);

  await crawler.onIdle(); 
  await crawler.close(); 
})();

What is the expected behavior?

Crawled urls should be skipped even if they come from the queue.

Please tell us about your environment:

• Version: lastest
• Platform / OS version: Centos 7.1
• Node.js version: v8.4.0