Expose response.redirected to FetchResponse

[t27duck]

I could be completely off-base, but in the known limitations section in the README, I don't think this code actually would work...

  const request = new FetchRequest('post', 'localhost:3000/my_endpoint', { body: { name: 'Request.JS' }})
  const response = await request.perform()
  response.redirected // => will always be false.

I am pretty sure response in this case is a FetchResponse and not a Response, so redirected wouldn't be defined.

I exposed redirect from the internal respose object in FetchResponse to at least make the code in the README correct.