Upgrade slice to 0.38

[jagill]

Previous version was 0.36. There was one minor incompatibility.

== RELEASE NOTES ==

General Changes
* Upgrade airlift/slice to 0.38.

[wenleix]

@jagill : Any plan to use https://github.com/prestodb/slice ? ;)

[jagill]

@wenleix This is a very small PR that does not change any philosophical orientation. prestodb/slice can be a follow-up commit, which will take advantage of the fact that this commit solves one backwards-incompatibility :)

[wenleix]

@jagill : Sounds reasonable. Just keep in mind you might have to backport some changes to prestodb/slice if we start to rely on features in newer version in airlift/slice :)

[wenleix]

LGTM.

[wenleix]

Merged #14014, thanks for the contribution!