Node 14.5 - process does not exit after all Threads terminated

Hi,

I found this library due to good wrapper around worker_threads which makes it easy to work with TS code and I am grateful for this :)

Anyway, I have some strange issue which I'd like to solve:
```typescript
const workers: FunctionThread[] = [];

for (const chunk of chunks) {
const worker = await spawn(new Worker("./coordinatorWorker"));
workers.push(worker);
worker(chunk);
}

await wait(1000);

await Promise.all(workers.map(Thread.terminate));
```

I would expect to process to finish, but it hangs with open handles, however it responds to ctrl+C.

I found 2 issues relating to that, but they were using a wrapper for old Node versions, so it was different.