Update dependency firebase-functions to v3

[renovate-bot]

This PR contains the following updates:

Package	Type	Update	Change
firebase-functions	devDependencies	major	2.3.1 -> 3.1.0
firebase-functions	dependencies	major	2.3.1 -> 3.1.0

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Release Notes

firebase/firebase-functions

v3.1.0

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• Adds region support for us-east4.

v3.0.2

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• bug where auth.UserRecord.metadata was undefined.

v3.0.1

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• Includes required types for functions SDK.

v3.0.0

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• [breaking change] The Firebase Functions SDK no longer supports Node 6. Developers must use Node 8.13.0 or higher.
• [breaking change] The Firebase Functions SDK no longer supports Firebase Tools SDK below version 6.8.0.
• [breaking change] FIREBASE_PROJECT environment variable is no longer supported and has been supplanted by FIREBASE_CONFIG.
• Fixed bug in Node 10 where events from Node 10 were not parsed properly resulting in undefined.
• Set GCLOUD_PROJECT from FIREBASE_CONFIG when missing.

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