Automated submodule update: vrs (#144)

Summary:
This is an automated pull request to update the first-party submodule for [facebookresearch/vrs](https://github.com/facebookresearch/vrs).

New submodule commit: facebookresearch/vrs@6b6ae79

Pull Request resolved: #144

Test Plan: Ensure that CI jobs succeed on GitHub before landing.

Reviewed By: georges-berenger

Differential Revision: D68120425

fbshipit-source-id: c2d1bb75d3e34f3a653fb1201a206f02e0842f5c