update `chunked_requests` submodule

hey @theengineear - I just merged a PR in to `chunked_requests` (https://github.com/chriddyp/chunked_requests/pull/5) - how do I update this repo? Are we still doing

```
$ make sync_chunked
```

a la https://github.com/plotly/python-api/blob/master/makefile#L46-L49?
