Support Uin8Array directly in update()

Uin8Array is emerging as the standard type for binary data in JavaScript, independent of Node.js's Buffer type. It would be very cool if a user could use Uin8Array input data directly in update() without wrapping it in a Buffer.

Right now this is prevented by an exception

```js
function throwIfNotStringOrBuffer (val, prefix) {
if (!Buffer.isBuffer(val) && typeof val !== 'string') {
throw new TypeError(prefix + ' must be a string or a buffer')
}
}

// ..

HashBase.prototype.update = function (data, encoding) {
throwIfNotStringOrBuffer(data, 'Data')
if (this._finalized) throw new Error('Digest already called')
if (!Buffer.isBuffer(data)) data = Buffer.from(data, encoding)
```

Here is an Uint8Array type checker for inspiration: https://github.com/iov-one/iov-core/blob/v2.2.4/packages/iov-encoding/src/typechecks.ts#L1-L26