corrected keyword argument name in docs for Tensor.scatter (#31617)
Summary:
See https://github.com/pytorch/pytorch/issues/31601
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31617
Differential Revision: D19268872
Pulled By: mruberry
fbshipit-source-id: 52f0213f4aab991fd549b7623556a2ced61631a6
