Handle stdin closing

[wmonk]

Description

When running react-script from something like Phoenix, when you stop the phoenix process, the react-script process hangs around in the background. Brunch and webpack have both implemented this.

Expected behavior

The process is stopped when stdin is closed.

Actual behavior

The process does not stop.

[gaearon]

Do you want to send a PR?

[SpaceK33z]

Not sure if it helps anyone, but we recently fixed the same issue in webpack-dev-server. See here. I imagine the fix in CRA would look a lot like this.