Mark sorted_vector swap as conditionally noexcept
Mark sorted_vector swap as conditionally noexcept

Summary: swap should be noexcept when possible

Reviewed By: yfeldblum

Differential Revision: D33198827

fbshipit-source-id: f8d52a21087b0346332359b66e1dc00f982ddbbb

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