CONTRIBUTORS: update for the Go 1.16 release

This update was created using the updatecontrib command:

	go get golang.org/x/build/cmd/updatecontrib
	cd gotip
	updatecontrib

With manual changes based on publicly available information
to canonicalize letter case and formatting for a few names.

For #12042.

Change-Id: I030b77e8ebcc7fe02106f0f264acdfb0b56e20d9
Reviewed-on: https://go-review.googlesource.com/c/go/+/291189


Trust: Carlos Amedee <carlos@golang.org>
Run-TryBot: Carlos Amedee <carlos@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Alexander Rakoczy <alex@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>