Fix compare_transform output
Fix compare_transform output

Summary:It always said "The dexes are equivalent", because the `diff | tee`
pipeline always returned success since tee did.  pipefail fixes that.

Reviewed By: dariorussi

Differential Revision: D3115603

fb-gh-sync-id: d7106056cc943df89157786377da47fbfd71c8a5
fbshipit-source-id: d7106056cc943df89157786377da47fbfd71c8a5

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex