Back to GPT3.5

I had updated the game to use GPT-4, rather than GPT-3.5,  2 weeks ago. This was a part of experiment to see how the game would run and what the cost would be. The result is, the GPT-4 usage costs ~$1 per user, even for an extremely short game like this. So I'll stick to the GPT-3.5 from now and continue observing the results.