add import for StrOutputParser

Author: Luke31

docs/platforms/python/integrations/langchain/index.mdx

@@ -78,6 +78,7 @@ Verify that the integration works by inducing an error:
 
 ```python
 from langchain_openai import ChatOpenAI
+from langchain_core.output_parsers import StrOutputParser
 import sentry_sdk
 
 sentry_sdk.init(...)  # same as above