Fix for issue #88

[koalter]

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[rgant]

This is not the correct fix for this problem.

The issue (for me) is that @angular/[email protected] is using firebase@9 which is still using @firebase/[email protected] but rxfire is expecting @firebase/firestore@4.

  └─┬ [email protected]
    ├─┬ @firebase/[email protected]
    │ └── @firebase/[email protected] deduped
    └── @firebase/[email protected]