Exit with error code on yarn-install failure (#292)
Exit with error code on yarn-install failure (#292)

Summary:
If installation fails, we should exit with an error code and not just a
message. This should help narrow down the CI failures, too.
Pull Request resolved: https://github.com/facebook/flipper/pull/292

Reviewed By: danielbuechele

Differential Revision: D10255759

Pulled By: passy

fbshipit-source-id: a6b033deadf11069e6c5665870a811ae2d0ec5ef

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