promisify

- [ ] return promise if callback function isn't specified.

```js
const {data} = await client.send(path, query, options);
...
```

- [ ] auto cancel option with same parameters.

```js
client.send(path, query, {autoCancel: true}, (err, data) => {
  //  if same path request is already called until this async callback.
  assert(err.message == 'AutoCancelled');
});
```