Fixed missing code block container
Fixed missing code block container

Summary: A missing code block closing back tick cause the documentation's layout to be incorrect.

Reviewed By: jknoxville

Differential Revision: D12948908

fbshipit-source-id: 8e9496d2bac81a49b39aed3a2c97ff6a20c71241

facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper