Update firebase.json

[chunhtai]

breaking change doc for flutter/packages#4227

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[sfshaza2]

Thanks, @chunhtai. It sounds like we'll also need a breaking change page?

[chunhtai]

Thanks, @chunhtai. It sounds like we'll also need a breaking change page?

Did you mean an entry in here? https://docs.flutter.dev/release/breaking-changes

This is for go_router, a first party package, not for flutter framework. I think this doesn't need one?