number: add plural integration also added consideration to use only VisibleDigits interface instead of plural.Interface. Change-Id: Ibb2a9a0eddc3f6fe7689b7fa3268f2bf0c8a97dc Reviewed-on: https://go-review.googlesource.com/60771 Run-TryBot: Marcel van Lohuizen <mpvl@golang.org> Reviewed-by: Nigel Tao <nigeltao@golang.org>