[jhuleatt]

Fixes #321

Description

Remove concurrent mode features from quickstart so that it works with stable builds of React

[ngocdaothanh]

@jhuleatt I'm new to reactfire. I've read the code in your PR. Can you please explain why in docs/quickstart.md you write this:

const { status, data } = useFirestoreDocData(burritoRef);

But in docs/quickstart-concurrent-mode.md you write this:

const burrito = useFirestoreDocData(burritoRef);

Why the same function useFirestoreDocData returns 2 different results?