cmd/benchstat: update golden testdata to match current behavior

Change-Id: I268e3731b51b2c7cb327fc47913058490c439d6a
Reviewed-on: https://go-review.googlesource.com/36610
Run-TryBot: Quentin Smith <quentin@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
5 files changed