Promise.all ?

Hi,

if you want users to ship small bundle sizes, would it be an idea to reference [Promise.all()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all) in the docs ?

Just for fun I recreated run-parallel with Promise.all() and ended up with:

```javascript
function runParallel (tasks, cb) {
const safecb = cb || (() => {})
if (Array.isArray(tasks)) {
// array
Promise.all(tasks.map(item => new Promise(
(resolve, reject) => item((err, result) => err ? reject(err) : resolve(result))
)))
.then(results => safecb(null, results))
.catch(err => safecb(err, null))
} else {
// object
Promise.all(Object.keys(tasks).map(item => new Promise(
(resolve, reject) => tasks[item]((err, result) => err ? reject(err) : resolve([item, result]))
)))
.then(results => safecb(null, Object.fromEntries(results)))
.catch(err => safecb(err, null))
}
}
```

This meets all tests except for one:

```javascript
test('functions that return errors (object) w/ partial results', function (t) {
t.plan(4)

const tasks = {
one: function (cb) {
t.pass('cb 1')
cb(null, 1)
},
two: function (cb) {
setTimeout(function () {
t.pass('cb 2')
cb(new Error('oops'))
}, 100)
}
}

parallel(tasks, function (err, results) {
t.ok(err instanceof Error)
t.deepEqual(results, { one: 1, two: undefined })
})
})
```
However that use case might be better off with [Promise.allSettled](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/allSettled)

Kind regards,
Hans