Add node-stream.js to react-dom's package.json files entry

[aickin]

In #10024, I added node-stream.js to react-dom's distribution, but I didn't realize that react-dom's package.json specifies which files are to be uploaded to the npm registry. As a result, if we tried to publish react-dom right now out of master, node-stream.js would not be a part of the package.

This PR fixes that. Sorry!

[magicmark]

@gaearon when/will this be available in a future release? It doesn't seem to be in 16.0.0-beta.5.

https://unpkg.com/[email protected]/package.json

(It was in 16.0.0-beta.2 - https://unpkg.com/[email protected]/package.json)

(The docs reference this API, which appears to have been recently updated)

Thanks so much!

[gaearon]

@magicmark In the latest release, they're just available directly on react-dom/server.