ONNX: fix bug in export of cumsum operator (#40044)
Summary:
The "cast" operator is currently added after the cumsum operator, but it should be added before, since torch.cumsum supports more types than ONNX (specifically, bool).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40044
Reviewed By: hl475
Differential Revision: D22158013
Pulled By: houseroad
fbshipit-source-id: e6c706572b9b8de880d4d71eaa132744ef01ad4d
