internal/number: fix rounding with DigitShift

Change-Id: I52454e27295200f1afcfea471f5020257af6d13b
Reviewed-on: https://go-review.googlesource.com/60590
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2 files changed