v0.5.9: dotslash_oss: Publish 0.5.9 (#126)

Summary:
Pull Request resolved: https://github.com/facebook/dotslash/pull/126

TSIA

Reviewed By: dtolnay

Differential Revision: D100198340

fbshipit-source-id: de9d4a9c4be809ec74a5f4fceffbcd86fe907126