Fix typo in error message (#2622)

langchain/llms/openai.py

@@ -223,7 +223,7 @@ class BaseOpenAI(BaseLLM):
         except ImportError:
             raise ValueError(
                 "Could not import openai python package. "
-                "Please it install it with `pip install openai`."
+                "Please install it with `pip install openai`."
             )
         if values["streaming"] and values["n"] > 1:
             raise ValueError("Cannot stream results when n > 1.")