rust-shed: change the workspace member definition to point to the newly moved project directories
rust-shed: change the workspace member definition to point to the newly moved project directories

Summary: The projects have been moved to a "shed/" subdirectory, so the root Cargo.toml with workspace has to be adjusted to that move.

Reviewed By: farnz

Differential Revision: D18807189

fbshipit-source-id: 0fd66fa7edd38ab4fdf905872f38fac57ae0230e

facebook/bistro,facebook/bistro,facebook/bistro,facebook/bistro,facebook/bistro,facebook/bistro