Update dependency firebase-admin to v4

Thalia Technicie
2020-02-27T09:10:08+01:00

This MR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [firebase-admin](https://firebase.google.com/docs/admin/setup/) ([changelog](https://firebase.google.com/support/release-notes/admin/python...

This MR contains the following updates:

Package | Type | Update | Change
firebase-admin (changelog) | dependencies | major | 3.2.1 -> 4.0.0

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