Shift folly/gen:string out of folly/gen:gen
Shift folly/gen:string out of folly/gen:gen

Summary: As-per title

Reviewed By: yfeldblum

Differential Revision: D5761613

fbshipit-source-id: 864ac2499808c5df3a1dcbb91bc44126b6d9a972

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