Error from different key is returned

[nico-hyperjump]

Bug report

Description / Observed Behavior

What kind of issues did you encounter with SWR?

When a request takes long to load, useSWR returns the error from the previous request, even though the keys are different.

Expected Behavior

How did you expect SWR to behave here?

useSWR should not return error from a different key.

Repro Steps / Code Example

1. Use Chrome
2. Install URL Throttle chrome extension to simulate slow network for a certain URL.
3. Enable the extension and add this url: https://pokeapi.co/api/v2/pokemon/ditto with 10000 ms delay. Toggle on the Enabled switch.
4. Open the sample in this Codesandbox: https://codesandbox.io/s/async-sound-9n2xm?file=/src/App.js
5. First type in the input text: fafafa, or any non-pokemon text.
6. The text: Error searching fafafa: fafafa not found will appear.
7. Next, enter in the input text: ditto.
8. Since we add 10-second delay to the url to search for ditto, the request will take 10 seconds to finish. So I expect the text Searching ditto will appear, but instead the text: Error searching ditto: dfadfa not found appears. It seems useSWR returns the error from the previous key, fafafa.
9. After 10 seconds, the error text disappears as expected and the response is displayed.

Since the key changes, useSWR should not return error from previous request imo.

Additional Context

SWR version: 0.3.9

[shuding]

Thanks for the detailed repro!