RC.8 fails on ng build --prod

[codediodeio]

Version info

Angular: 6.0.1
Firebase: 5.0.2
AngularFire: 5.0.0-rc.8.0

How to reproduce these conditions

1. Follow AngularFire2 setup instructions
2. Run ng build --prod

Debug output

ERROR in Error during template compile of 'AppModule'
Function calls are not supported in decorators but 'AngularFireModule' was called.

Expected behavior

Build should run successfully.

Actual behavior

Build fails only in production (AOT)

Problem

I don't think the Angular compiler can analyze code dynamically in initializeApp. These lines are the source of the problem

https://github.com/angular/angularfire2/blob/a8414f5d62ec073db760e0b7e9346e4d946bd3a3/src/core/firebase.app.module.ts#L50-L51

Possible Solution?

Require the second arg to initializeApp to be a FirebaseAppConfig object and remove the string union type.

[codediodeio]

Just noticed this is a duplicate. Will close for #1635