Switch to torch.nn.functional.gelu when available
Switch to torch.nn.functional.gelu when available

Summary: Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/735

Differential Revision: D16377046

Pulled By: myleott

fbshipit-source-id: 9725d4a3ce6b2fc8cee0b1d1cb8921f9d59c551a

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq