Removed comma after last value in object

[PiusNyakoojo]

Removed comma after last value in the object passed to defaultFirebase( )

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Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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[PiusNyakoojo]

I signed it!

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