Automated submodule update: vrs (#137)

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@b490899

Pull Request resolved: #137

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

Reviewed By: georges-berenger

Differential Revision: D67198007

fbshipit-source-id: d22c43d565b2193fedf4789f8e333793852c2da3