doc/go1.10: update release notes for recent commits

Change-Id: Id6ced9a6c76131263041cdaf5ed17479be075fa6
Reviewed-on: https://go-review.googlesource.com/82075
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>