@nitgeek's answer is correct. It needs to be upper case but I think you may also need to install the dependency so that it is available for your code.

https://github.com/langchain-ai/langchain/blob/master/libs/community/langchain_community/llms/ollama.py#L398

https://pypi.org/project/langchain-community/

Also make sure that you have the langchain_community community module installed via pip