Fix docstring for nn.ELU (#70574)
Summary:
Fixes nn.ELU's docstring problem reported at https://github.com/pytorch/pytorch/issues/70498.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70574
Reviewed By: VitalyFedyunin
Differential Revision: D33404696
Pulled By: albanD
fbshipit-source-id: 1ffcba3fdeadf88a4433e9168c42ddb252e833e9
