Fix APIRemovedInV1 error by downgrading OpenAI library to v0.28

[alexfazio]

This commit resolves the APIRemovedInV1 error in the Google Colab notebook by downgrading the OpenAI Python library to version 0.28. The error was caused by attempting to access the deprecated openai.ChatCompletion method in versions 1.0.0 and above.

Pinning the library to the older version ensures compatibility with the existing codebase and allows the code to function correctly without accessing the deprecated method.

---------------------------------------------------------------------------
APIRemovedInV1                            Traceback (most recent call last)
[<ipython-input-11-5fb2904844c6>](https://localhost:8080/#) in <cell line: 1>()
----> 1 generate_optimal_prompt(description, test_cases, NUMBER_OF_PROMPTS, use_wandb)

2 frames
[/usr/local/lib/python3.10/dist-packages/openai/lib/_old_api.py](https://localhost:8080/#) in __call__(self, *_args, **_kwargs)
     37 
     38     def __call__(self, *_args: Any, **_kwargs: Any) -> Any:
---> 39         raise APIRemovedInV1(symbol=self._symbol)
     40 
     41 

APIRemovedInV1: 

You tried to access openai.ChatCompletion, but this is no longer supported in openai>=1.0.0 - see the README at https://github.com/openai/openai-python for the API.

You can run `openai migrate` to automatically upgrade your codebase to use the 1.0.0 interface. 

Alternatively, you can pin your installation to the old version, e.g. `pip install openai==0.28`

A detailed migration guide is available here: https://github.com/openai/openai-python/discussions/742
<img width="1396" alt="Screenshot · Arc gpt_prompt_engineer ipynb - Colab · 2024-04-10 at 19 31 59@2x" src="https://github.com/mshumer/gpt-prompt-engineer/assets/34505954/23c46d88-4072-4134-a4fd-83c6274d566b">