Avoid stale state updates

[jackfranklin]

I think that useQuery needs to track if it's been unmounted to avoid stale updates.

We're seeing:

Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all sub

And I think it's coming from useQuery. I think the setState calls need to be conditional based on some variable that we toggle from true to false when the component gets updated.

Much like this usePromise example: https://gist.github.com/mjackson/05c7749430d0ec87b66612733805bad6.

Happy to make the PR if you're happy with this proposal?

[andyrichardson]

This should be easily doable using a ref on mount/unmount.

[kitten]

#256 will additionally ensure that we don't regress on this