Update sharegpt.py

Resolves the double EOS token issue at the end of prompts when using Chatml template with shareGPT.py. 

#922 (comment)

src/axolotl/prompt_strategies/sharegpt.py

@@ -12,8 +12,8 @@
         system_template="<|im_start|>system\n{system_message}",
         system_message="You are a helpful assistant.",
         roles=["<|im_start|>user", "<|im_start|>assistant"],
-        sep_style=SeparatorStyle.CHATML,
         sep="<|im_end|>",
+        stop_str="<|im_end|>"
     )
 )