Typo in tutorial.md
Typo in tutorial.md

Summary: per title

Reviewed By: mihaelao

Differential Revision: D4907089

fbshipit-source-id: 7cf83b4e796bfd457fac962c7201332d93a5e4ac

facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho