This also allows digits in class decorators, to also match macros like
V8_EXPORT_PRIVATE.

Note: I uploaded a pull request for the (previous) upstream at
https://github.com/google/styleguide/pull/422, but then was told that
that repository is not maintained any more.

R=jochen@chromium.org

Bug: chromium:916550

Change-Id: I24cd1829b794b296be8e0c2829271c746751ee1c
Reviewed-on: https://chromium-review.googlesource.com/c/1383472
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>