Summary:
In Node v6 there is no `final` function: https://nodejs.org/docs/v6.13.1/api/stream.html#stream_simplified_construction.
It's not a problem however because we can preferentially use the `finish` event, that makes it more consistent with how `createReadStream` is implemented. I also added closing the fs on `error` events, as specified in the docs.
**Test plan**
yarn jest
Closes https://github.com/facebook/metro/pull/150
Reviewed By: rafeca
Differential Revision: D7215708
Pulled By: jeanlauliac
fbshipit-source-id: 80921a245c8c87085a2ba83b84b1156a60aa1fb3
