my_function.gather(tqdm=False) is broken

* lox version: `0.11.0`

### Description

```
Traceback (most recent call last):
  File "/usr/lib/python3.8/concurrent/futures/_base.py", line 328, in _invoke_callbacks
    callback(self)
  File "thread.py", line 105, in tqdm_callback
    tqdm.update(1)
AttributeError: 'bool' object has no attribute 'update'
```