I can not deploy specified hosting target

## Affected builder image
gcr.io/cloud-builders-community/firebase

## Expected Behavior
I can deploy specified hosting target.

## Actual Behavior
I can not deploy specified hosting target.
I got this error.
```
textPayload: "Step #3 - "deploy to firebase hosting": Error: Deploy target $MY_HOSTING_TARGET not configured for project $MY_FIREBASE_PROJECT_ID. Configure with:"
```

## Steps to Reproduce the Problem

1. Deploy with this cloudbuild.yml
```
- name: gcr.io/MY_GCP_PROJECT/firebase
id: 'deploy to firebase hosting'
args: [ 'deploy', '--project=MY_FIREBASE_PROJECT_ID', '--only=hosting:MY_HOSTING_TARGET' ]
dir: admin-tool
```

firebase.json like this
```
{
"hosting": {
"target": "MY_HOSTING_TARGET",
"public": "build",
"ignore": [
"firebase.json",
"**/.*",
"**/node_modules/**"
],
"rewrites": [
{
"source": "**",
"destination": "/index.html"
}
]
}
}

```
3.
4.

## Additional Info