[App Engine] TS : Adding the missing node type definition

[Alutun]

The Typescript example is actually not working.
When App Engine is running the npm run gcp-build

It will throw erros like this one :

Step #6 - "builder": index.ts(17,21): error TS2580: Cannot find name 'process'.

The package.json is missing the node Types definitions module.

My pull request is fixing that.

Best

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[Alutun]

@googlebot I signed it!

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