Automated submodule update: vrs (#128)

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@3c709a8

Pull Request resolved: #128

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

Reviewed By: georges-berenger

Differential Revision: D65933103

fbshipit-source-id: c790ab88c83b134ea5067c72393dc5220b1097d8