Use JS terminology for the result of `pending` in README

It's really weird to say that `pending()` should return a Tuple in JavaScript. The language has no concepts of Tuples, and when you say "it should return a Tuple of `{ promise, fulfill, reject }`" I immediately think about a Haskell Tuple, which would be `( promise, fulfill, reject )`, and close to the JS idiom `[ promise, fulfill, reject ]`.

This, as it turns out, is quite unintuitive for people who are used to the concept of tuples (and working with them in other languages like Haskell or Python), who will have their `pending` function return such List, just to find out quite a while afterwards that you should actually be returning an Object, as I've discovered from reading @briancavalier's avow tests (https://github.com/briancavalier/avow/blob/master/test/avow-adapter.js#L4-L11)