.redirects(number) keeps waiting, doesn't resolve in v6.2.2

Hi,

we have something like this in tests:

```ts
const response = await supertest(getServer()).get('/auth').redirects(2);
```

And after update to v 6.2.2 the tests just hand on this line.
It doesn't resolve, doesn't throw, just hangs in there till the test timeout expires.

Could it be somehow related to the change in the superagent https://github.com/visionmedia/superagent/commit/e196345074f57987c166283c302d06d661744f14?
I don't actually see how it would affect `.redirects()`, but I don't see any other change.

I've tried to force superagent back to 7.0.2, and tests are working as expected.

Start with the reported test expression, `await supertest(getServer()).get('/auth').redirects(2)`, and reproduce the hang on v6.2.2. Compare it with the working superagent 7.0.2 setup and inspect the linked superagent change for the redirect path. Done means `.redirects(2)` resolves or throws instead of waiting for the test timeout.

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