GitLab

Adds pyserial 3.4 to the .vpython file. This is currently only used
by the VR motion-to-photon latency test.

Bug: 812428
Change-Id: I56644689177394dfdba727be41bdf792386e0f2e
Reviewed-on: https://chromium-review.googlesource.com/943923Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540354}