use lowest() in numeric traits
use lowest() in numeric traits

Summary:
The numeric functions `less_than` and `greater_than` are intended for integer use but, technically, they are not constrained to integer use. If they are used with floating-point types, `min()` does not do the expected thing so use use `lowest()`.

Fixes: https://github.com/facebook/folly/issues/1604.

Reviewed By: iahs

Differential Revision: D29069620

fbshipit-source-id: 369bd59338b889cb1ec0f56d232a3775500573d0

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