Summary:
Currently the CI on release branch uses nightly PyTorch release. This PR changes it to use RC PyTorch release.

See the CI result for when the PR is landed (nightly channel): https://github.com/pytorch/data/runs/6867662390?check_suite_focus=true#step:8:3
See the CI result of the PR for release branch (test channel): https://github.com/pytorch/data/runs/6867788289?check_suite_focus=true#step:8:3

Pull Request resolved: https://github.com/pytorch/data/pull/514

Reviewed By: NivekT

Differential Revision: D37116635

Pulled By: ejguan

fbshipit-source-id: 2dbe65da8121dfbd39690c83c2e1ca6cb70c0087