Firestore emulator live update on rules file changes

[samtstern]

Watches the file specified in firebase.json for changes and updates the rules in the emulator.

Successful Change

Unsuccessful Change

I styled the error printing based on what the TypeScript compiler does in "watch" mode.

[ryanpbrewster]

What is the behavior you'd expect if you have a syntax error in your rules?

[samtstern]

@ryanpbrewster I would expect the emulator to reject the ruleset with a 4xx error ... what does it actually do?

[coveralls]

Coverage decreased (-0.4%) to 61.644% when pulling 7bcf35a on ss-rules-watcher into 89614cb on master.

[ryanpbrewster]

It does indeed fail, and as a result does not update the rules. You end up in a situation where you're editing your rules and the edits aren't taking effect. Unless you look at the emulator suite logging (often in the background or in some other terminal) you won't be able to figure out why.

[yuchenshi]

LGTM. Much better!

[samtstern]

The Travis build passed but I think the webhook back to GitHub must have been dropped:
https://travis-ci.org/firebase/firebase-tools/builds/553869724?utm_source=github_status&utm_medium=notification

So I am going to merge this.