"Error: Not in a Firebase app directory (could not locate firebase.json)", but it is there?¿

## Affected builder image

`gcr.io/cloud-builders-community/firebase`

## Expected Behavior

command `firebase deploy ` working

## Actual Behavior

I get the error:

> Error: Not in a Firebase app directory (could not locate firebase.json)

Even though there is a firebase.json in the current directory.

## Steps to Reproduce the Problem

1. build docker image
2. ` docker run --rm -e GOOGLE_APPLICATION_CREDENTIALS=./backend/videosdb/keys/testing.json firebase deploy --project videosdb-testing --only=hosting`
3. profit

## Additional Info

Also, if I just switch to using my local firebase binary, it deploys well. I.E. Removing the `"docker run --rm -e"` part of the above command.

Thank you for your time. I am avaiable for testing.

Start by reproducing the listed docker run command with gcr.io/cloud-builders-community/firebase and check whether the container's current directory can see firebase.json. Compare this with the local Firebase binary behavior; the issue is done when the containerized firebase deploy locates the existing file and deploys successfully.

Written by the indexing model from the issue text.