Dataset `rel-stack` with task `user-post-related` doesn't exist

[akihironitta]

It should instead be:

- user-post-related
+ post-post-related

https://relbench.stanford.edu/datasets/rel-stack/

[rishabh-ranjan]

Thanks for reporting! @kexinhuang12345 can you please update?

[kexinhuang12345]

just updated!