Angularfire: FirebaseOptionsToken missing in 6.0

[alexfung888]

Version info

Angular:
9.1.1

Firebase:
7.13.2

AngularFire:
6.0.0

How to reproduce these conditions

npm start

Failing test unit, Plunkr, or JSFiddle demonstrating the problem

import { AngularFireModule
  , FirebaseOptionsToken
} from '@angular/fire';
...
  providers: [  { provide: FirebaseOptionsToken, useValue: environment.firebase }  ],
<!-- 


### Debug output
@angular/fire/angular-fire"' has no exported member 'FirebaseOptionsToken'.

### Expected behavior

compile and run

### Actual behavior

compile failure

I am not sure whether this is supposed to be part of 

Dropped runOutsideAngular, runInZone, FirebaseZoneScheduler, and the Firebase* type aliases

behaviour, but without the FirebaseOptionsToken how should we code the provider statement?
Do we fall back to the pre version 5 method of 
```ts
  imports: [ AngularFireModule.initializeApp(environment.firebase) ],

?

[jamesdaniels]

FirebaseOptionsToken is now exported only as FIREBASE_OPTIONS, if you switch over to that it should work fine.