fix default generation_config

generation_config.json

@@ -11,6 +11,6 @@
   "stop_words_ids": [[151643]],
   "do_sample": true,
   "top_k": 0,
-  "top_p": 0.8,
+  "top_p": 0.5,
   "transformers_version": "4.31.0"
 }