Summary:
Found with modernize-use-equals-default
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Pull Request resolved: https://github.com/facebook/folly/pull/1291

Reviewed By: markisaa

Differential Revision: D19229643

Pulled By: yfeldblum

fbshipit-source-id: 69f0bd4f55ea5a3697ab176aab80683b99b4e11c