Update cohere.py (#795)

When stop tokens are set in Cohere LLM constructor, they are currently
not stripped from the response, and they should be stripped

Author: bair82

langchain/llms/cohere.py

@@ -122,6 +122,6 @@ def _call(self, prompt: str, stop: Optional[List[str]] = None) -> str:
         text = response.generations[0].text
         # If stop tokens are provided, Cohere's endpoint returns them.
         # In order to make this consistent with other endpoints, we strip them.
-        if stop is not None:
-            text = enforce_stop_tokens(text, stop)
+        if stop is not None or self.stop is not None:
+            text = enforce_stop_tokens(text, params["stop_sequences"])
         return text