[DataPipe] Fixing MapDataPipe docstrings (#72476)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/72476
To render the change in documentation, please pull down this PR and build the doc in `TorchData`.
Test Plan: Imported from OSS
Reviewed By: ejguan
Differential Revision: D34078078
Pulled By: NivekT
fbshipit-source-id: f478d5a901f8364ab6de1fd4bf8a8ab1036b2231
(cherry picked from commit e00a9967e9cb4372efed32e0600751e6f726c5cc)
