text: Title: AttributeError: module 'tiktoken' has no attribute 'encoding_for_model'
  Body: Getting the following error when launching the app
  
  `File "C:\Users\xxx\Anaconda3\lib\site-packages\streamlit\runtime\scriptrunner\script_runner.py", line 565, in _run_script
      exec(code, module.__dict__)
  File "C:\Users\xxx\ask-my-pdf\src\gui.py", line 20, in <module>
      import model
  File "C:\Users\xxx\ask-my-pdf\src\model.py", line 12, in <module>
      import ai
  File "C:\Users\xxx\ask-my-pdf\src\ai.py", line 39, in <module>
      tokenizer_model = openai.model('text-davinci-003')
  File "C:\Users\xxx\Anaconda3\lib\site-packages\ai_bricks\api\openai.py", line 30, in model
      return _class(name, **kwargs)
  File "C:\Users\xxx\Anaconda3\lib\site-packages\ai_bricks\api\openai.py", line 57, in __init__
      self.encoder = tiktoken.encoding_for_model(name)`