folly/executors: fix extraneous semi-colon
folly/executors: fix extraneous semi-colon

Reviewed By: yfeldblum

Differential Revision: D13056552

fbshipit-source-id: 910296cda7d392972a48c8fa3e425b4bdeaa5d26

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly