Fix docstring for nn.Tanh (#70577)
Summary:
Fixes nn.Tanh's docstring problem reported at https://github.com/pytorch/pytorch/issues/70498.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70577
Reviewed By: VitalyFedyunin
Differential Revision: D33408564
Pulled By: albanD
fbshipit-source-id: 2008cb55ef72b4b057d8d68e4505956aaf6cc3fa
