fix https://github.com/hwchase17/langchain/issues/2392 (#2393)
As noted in
https://github.com/ggerganov/llama.cpp/blob/master/migrate-ggml-2023-03-30-pr613.py,
Authors from `llama.cpp` caused a breaking change to the file format on
2023-03-30 in: https://github.com/ggerganov/llama.cpp/pull/613
Therefore, we need further use `migrate-ggml-2023-03-30-pr613.py` to
convert the llama model.