fix for clang-tidy (#16164)
Summary:
It turns out that clang-tidy is bundled with travis's standard trusty distribution, so no need to install it manually.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16164
Differential Revision: D13738986
Pulled By: suo
fbshipit-source-id: d0cd76c615625b2ed7f18951289412989f15849d
