Missing `matplotlib` dependency

[michellewang]

(Saw this yesterday together but I thought I would create an issue so that we don't forget)

When running src/model_openai.py, I get an error because matplotlib isn't installed:

Traceback (most recent call last):
  File "/data/origami/michelle/projects/LoxLM/src/model_openai.py", line 1, in <module>
    from utils.multi_example_selector import MultiExampleSelector, Example
  File "/data/origami/michelle/projects/LoxLM/src/utils/multi_example_selector.py", line 13, in <module>
    import matplotlib.pyplot as plt
ModuleNotFoundError: No module named 'matplotlib'