Update token spacing for mistral conversation.py (#2872)

Author: thavens

fastchat/conversation.py

@@ -982,7 +982,7 @@ def get_conv_template(name: str) -> Conversation:
 register_conv_template(
     Conversation(
         name="mistral",
-        system_template="[INST]{system_message}\n",
+        system_template="[INST] {system_message}\n",
         roles=("[INST]", "[/INST]"),
         sep_style=SeparatorStyle.LLAMA2,
         sep=" ",