[QUESTION] Supported Node versions and required deps

[ronkorving]

What / Why

I noticed in 9a290ec that Node versions older than 8 is not quite supported anymore by this package. If that is the case, I think you should be able to replace the util-promisify dependency by Node's built-in util.promisify, right? I was looking at my NPM dependency tree (npm ls) and noticed how big a tree sits below util-promisify, so it got me curious. Thanks!