cmd/release: fix flag
cmd/release: fix flag

Change-Id: I62dbbe1d4a18f34d950e5c17e7a5e9567dfe84eb
Reviewed-on: https://go-review.googlesource.com/5223
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

proppy/build,golang/build,evandbrown/build,evandbrown/build,golang/build,proppy/build,proppy/build,evandbrown/build,golang/build,proppy/build,golang/build