fix: unhandled promise rejection when async work done after handshake (…

…#2)

If you do async work after invoking it-handshake but before awaiting
on any of the fields of the response, an unhandledPromiseRejection can
occur if the `stream.sink` method rejects.

This manifests itself in libp2p vis `multiformats/js-multistream-select`
as:

```js
(node:82951) UnhandledPromiseRejectionWarning: Error: already piped
    at Object.sink (node_modules/it-pair/index.js:10:24)
    at module.exports (node_modules/it-handshake/src/index.js:15:30)
    at module.exports (src/select.js:10:57)
    at Dialer.select (src/index.js:27:12)
    at Context.<anonymous> (test/dialer.spec.js:43:26)
```

Also:

- Updates all deps
- Removes node Buffers in favour of Uint8Arrays