Fix build warnings
Fix build warnings

Summary: Adding braces in the string initialization to avoid build warnings

Reviewed By: Gownta

Differential Revision: D34936299

fbshipit-source-id: 64390421ae6a38dcc7a6c04ba04b20a44de81a1d

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