Fix checkpoint name
# What does this PR do?

Fix some `eleutherai/gpt-neox-20b` to `EleutherAI/gpt-neox-20b`.

The uppercase vs. lowercase in the checkpoint name matters, otherwise I got error like

`is not a local folder and is not a valid model identifier listed on`
cc @zphang  :-)<|||||>_The documentation is not available anymore as the PR was closed or merged._