Update README.md

Fix dead link. chatml.md file removed from openai/openai-python from v1.0.0 onwards.

README.md

@@ -21,7 +21,7 @@ We adopted exactly the same architecture and tokenizer as Llama 2. This means Ti
 
 #### This Model
 This is the chat model finetuned on top of [PY007/TinyLlama-1.1B-intermediate-step-480k-1T](https://huggingface.co/PY007/TinyLlama-1.1B-intermediate-step-480k-1T). 
-The dataset used is [OpenAssistant/oasst_top1_2023-08-25](https://huggingface.co/datasets/OpenAssistant/oasst_top1_2023-08-25) following the [chatml](https://github.com/openai/openai-python/blob/main/chatml.md) format.
+The dataset used is [OpenAssistant/oasst_top1_2023-08-25](https://huggingface.co/datasets/OpenAssistant/oasst_top1_2023-08-25) following the [chatml](https://github.com/openai/openai-python/blob/v0.28.1/chatml.md) format.
 #### How to use
 You will need the transformers>=4.31
 Do check the [TinyLlama](https://github.com/jzhang38/TinyLlama) github page for more information.