Fix typo in doc block
Fix typo in doc block

Summary: Self-explanatory.

Reviewed By: Mizuchi

Differential Revision: D26409923

fbshipit-source-id: 7288a0dddf622fa2c8bb0cb5aee4f731da6fb5aa

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift