[P4] Update Firebase dependency to support EU and AP regions

[willroberts]

Summary

Creating a Firebase Realtime Database in EU (Belgium) or AP (Singapore) results in a Firebase URL which does not end in firebaseio.com, which is required by our current Firebase dependency.

We should upgrade the firebase package to a version which supports these endpoints.

[willroberts]

This may be the version we need: https://firebase.google.com/support/release-notes/js#version_7145_-_may_21_2020

We should probably avoid version 8.x (which switches to ES6 modules) and 9.x (which changes the package structure to a modular format, requiring code changes) for now.

[willroberts]

Upgrading directly to 7.14.5 with no other changes produces an error:

Unhandled rejection [1]</App.getMinBrowserVersions/<@http://localhost:3000/duelyst.js:3491:28

And a warning:

It looks like you're using the development build of the Firebase JS SDK.
When deploying Firebase apps to production, it is advisable to only import
the individual SDK components you intend to use.

It seems version 7.x also requires code changes.