benchmarks/stats: added/fixed copyrights, typo fixes

Change-Id: Icb29a8a2d4f56fb303806099d7fef873f6efd932
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/321962
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
5 files changed