Use `repo.anaconda.com` instead of `repo.continuum.io` (#36201)
Summary:
Per https://github.com/conda/conda/issues/6886 `repo.anaconda.com` should have been used since Feb 2019
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36201
Test Plan: CI
Differential Revision: D20910667
Pulled By: malfet
fbshipit-source-id: 3a191e2cae293e6f96dbb323853e84c07cd7aabc
