Add torch.nn.GELU for GELU activation (#28944)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28944
Add torch.nn.GELU for GELU activation
Test Plan: buck test mode/dev-nosan //caffe2/test:nn -- "GELU"
Reviewed By: hl475, houseroad
Differential Revision: D18240946
fbshipit-source-id: 6284b30def9bd4c12bf7fb2ed08b1b2f0310bb78
