Add `Ellipsis` constant to the list of recognized tokens (#44959)
Summary:
Per https://docs.python.org/3.6/library/constants.html
> `Ellipsis` is the same as ellipsis literal `...`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44959
Reviewed By: suo
Differential Revision: D23785660
Pulled By: malfet
fbshipit-source-id: f68461849e7d16ef68042eb96566f2c936c06b0f
