Remove is-promise dependency?

[jplock]

Why not remove an external dependency on is-promise and implement:

function isPromise(obj) {
  return !!obj && (typeof obj === 'object' || typeof obj === 'function') && typeof obj.then === 'function';
}

in index.js itself.

[mdlavin]

I didn't want to try duplicating the logic of Promise detection if some other project provided the logic already. I don't want to keep up with the most appropriate way to detect a Promise as things change. If there is a better dependency to use I'm up for switching.