[sledge] Fix type of Context.fold_uses_of
[sledge] Fix type of Context.fold_uses_of

Reviewed By: jvillard

Differential Revision: D25756581

fbshipit-source-id: afb0e0509

facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,facebook/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,jvillard/infer