CBLT-319:  fix package name for windows sgw prepare-release stage

Change-Id: I24273519b1fc86f500308b3d23dee0cd41d0e91d
Reviewed-on: http://review.couchbase.org/38501
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>