cmd/release: update releaselet to specify arch on windows msi

Fixes golang/go#17602

Change-Id: Ia7873d6a5e0226833b2e16a3486bc71f183a8442
Reviewed-on: https://go-review.googlesource.com/34502
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed