fix contbuild (#16362)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16362
https://our.intern.facebook.com/intern/testinfra/diagnostics/281475065177800.844424930381786.1548397180/
Reviewed By: ezyang
Differential Revision: D13816639
fbshipit-source-id: 024117233f6d3bc6244013ca2ee1aea065560212
