build Linux binaries on centos7
build Linux binaries on centos7

Summary:
the prebuilt Linux binaries were built on a debian8 VM. this was released in 2015, but EOL in June 2020. meanwhile, centos7 was released in 2014 and is supported until 2024.

Flow v0.143.0 includes some C++ code that, when built in debian8, requires a newer libc++ than centos7 has.

switching the build to centos7 restores portability.

Pull Request resolved: https://github.com/facebook/flow/pull/8576

Reviewed By: Hans-Halverson

Differential Revision: D26006003

Pulled By: mroch

fbshipit-source-id: 9d0d6a1d9eb9b730d550420bb255ad06765c1391

mroch/flow,facebook/flow,facebook/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow,mroch/flow,mroch/flow,facebook/flow,facebook/flow