Polyfill for util.promisify in node versions < v8
node v8.0.0 added support for a built-in util.promisify: https://github.com/nodejs/node/pull/12442/
This package provides the built-in util.promisify in node v8.0.0 and later, and a replacement in other environments.
Note: this package requires a native ES5 environment, and for Promise to be globally available. It will throw upon requiring it if these are not present.