add support child frames

[Mavrin]

Summary

When I pass child frame instance to expectPuppeteer, I get error Frame is not supported.

  const frame = page.frames().find(frame => frame.name() === 'myframe');
  const text = expectPuppeteer(frame).toClick('.selector');

[gregberge]

Hello @Mavrin, thanks for your work, it is very good!

[yesmeck]

@neoziro Could you make a release?