Summary:
Promisify leads to weird types and sometimes unexpected runtime behaviour. Replacing it with the dep we use everywhere.
It's just really annoying that `stdout` is here explicitly `| null` which isn't the case in the default types.
Reviewed By: timur-valiev
Differential Revision: D31278303
fbshipit-source-id: eadbc49b287704e71a5ecba0d9a311eac91dc6f8
fe3eda024b