[Telemetry] Update WPR README.chromium

This CL updates README.chromium in third_party/webpagereplay to correspond to
the roll in crrev.com/1567603003

TBR=nednguyen

Review URL: https://codereview.chromium.org/1565833002

Cr-Commit-Position: refs/heads/master@{#367852}

tools/telemetry/third_party/webpagereplay/README.chromium

 Name: chromite
 Short Name: webpagereplay
 URL: https://github.com/chromium/web-page-replay
-Version: ac5d71a0938d98c82220398fbdc9036fdda1240f (commit hash)
+Version: baa1ef964a0758e14871be0676899335149a3d78 (commit hash)
 License: BSD
 License File: NOT_SHIPPED
 Security Critical: no