Removed node_modules from cleanup; updated firebase dependency

[paulywill]

Trying to follow the README.md instructions do not work.

As discovered in #53 by @juanmaguitar, by removing the node_modules in the cleanup line called by the build, the build will run successfully locally.

In addition, I had to update the firebase dependency to resolve an npm install: node-pre-gyp error.

After Changes:

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[paulywill]

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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Sign it.

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