cmd/release: supply SHA256 hash when uploading releases

Fixes golang/go#12057

Change-Id: Id66b1ec37a3d2dfb36aac6b70d8b70e537d4f3cb
Reviewed-on: https://go-review.googlesource.com/18353
Reviewed-by: Russ Cox <rsc@golang.org>
1 file changed