fix(schematics): firebase does not added to dependencies (#2479)

[lisp719]

• Refer to the correct object

Checklist

• Issue number for this PR: Running ng add @angular/fire does not add firebase to dependencies #2479
• Docs included?: no
• Test units included?: no
• In a clean directory, yarn install, yarn test run successfully? yes

Description

Fixed firebase to be added to dependencies when running ng add @angular/fire

Code sample

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[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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[lisp719]

@googlebot I signed it!

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[jamesdaniels]

Nice catch, we should try to get some coverage over this.