🐛 Docs Fixes [2 one-liners, examples broken] (#8519)
## Description:
1)Map reduce example in docs is missing an important import statement.
Figured other people would benefit from being able to copy 🍝 the code.
2)RefineDocumentsChain example also broken.
## Issue:
None
## Dependencies:
None. One liner.
## Tag maintainer:
@baskaryan
## Twitter handle:
I mean, it's a one line fix lol. But @will_thompson_k is my twitter
handle.
