Update path to pretrained yolox asset

[pjbull]

Videos weren't loading in latest version, and we were seeing a lot of these errors:

2021-12-17 01:11:44.274 | WARNING  | zamba.pytorch.dataloaders:__getitem__:118 - Video /data/blank3.mp4 could not be loaded. Using an array of all zeros instead.

Upon debugging, discovered this was because of the following stack trace:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.8/dist-packages/zamba/data/video.py", line 468, in load_video_frames
    mdlite = MegadetectorLiteYoloX(config=config.megadetector_lite_config)
  File "/usr/local/lib/python3.8/dist-packages/zamba/object_detection/yolox/megadetector_lite_yolox.py", line 88, in __init__
    checkpoint = torch.load(path, map_location=config.device)
  File "/usr/local/lib/python3.8/dist-packages/torch/serialization.py", line 594, in load
    with _open_file_like(f, 'rb') as opened_file:
  File "/usr/local/lib/python3.8/dist-packages/torch/serialization.py", line 230, in _open_file_like
    return _open_file(name_or_buffer, mode)
  File "/usr/local/lib/python3.8/dist-packages/torch/serialization.py", line 211, in __init__
    super(_open_file, self).__init__(open(name, mode))
FileNotFoundError: [Errno 2] No such file or directory: '/usr/local/lib/python3.8/dist-packages/zamba/object_detection/yolox/assets/yolox_nano_20210901.pth'

Looks like this was introduced when #167 was merged.

Added extra test to make sure YoloX can load so we will catch an error like this with CI in the future.

[github-actions]

🚀 Deployed on https://deploy-preview-172--silly-keller-664934.netlify.app

[codecov]

Codecov Report

Merging #172 (8d8b965) into master (380d23f) will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #172   +/-   ##
======================================
  Coverage    85.0%   85.0%           
======================================
  Files          30      30           
  Lines        1851    1851           
======================================
  Hits         1575    1575           
  Misses        276     276           

[r-b-g-b]

Looks good, sorry for missing that!