docs/updating_clang.md: Use the new linux-chromeos-dbg trybot

The old linux_chromium_chromeos_dbg_ng one doesn't exist anymore.

Bug: 732531
Change-Id: I792eabe3111431b113e5224037dbd0f9fd6ce5f1
Reviewed-on: https://chromium-review.googlesource.com/772908
Reviewed-by: Peter Collingbourne <pcc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516888}
1 file changed