Compiling Electron leads to firestore breaking due to grpc issues.

Hey there! I am currently developing a desktop application using electron that is able to run as an admin client for our managers at work. I've run into an issue with using firebase-admin where when electron is in dev mode it works fine, but when compiled into an exe format it breaks and the error it has is saying that I need to "pass auth instance to grpc-fallback-client" and its coming from `new GrpcClient` looking further into the code about how this is made its a google-gax client.

Not sure if this is the correct area to put this but I've tried other areas and found nothing. The only similar issue I have seen is googleapis/google-cloud-node-core#445

#### Environment details

- OS: Windows
- Node.js version: 8.16.1
- npm version: 6.4.1
- `google-gax` version: 1.3.0

#### Steps to reproduce
(very custom way to hit this and I don't really know how to walk someone through getting to this exact error)
1. Have an Electron app that you can compile to exe
2. inside the main.js or type script file add an admin client from `firebase-admin`
3. Authenticate your admin client
4. Try and pull a collection from firestore

Thanks!

Inizia riproducendo l’applicazione Electron Windows pacchettizzata descritta nei passaggi, utilizzando il client Firestore di firebase-admin da main.js o dal punto di ingresso TypeScript. Traccia l’errore segnalato a partire da new GrpcClient in google-gax e confronta l’esecuzione in sviluppo con quella compilata. Il lavoro è completato quando l’applicazione compilata esegue l’autenticazione e recupera una raccolta Firestore senza l’errore grpc-fallback-client.

Scritto dal modello di indicizzazione a partire dal testo della issue.