Consistent with similar change of style in the crypto repository:
http://golang.org/cl/43511

Change-Id: Ib158c52a2649dcbbe9eb92f2bdb9d289e0dcc7bf
Reviewed-on: https://go-review.googlesource.com/53474Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
Reviewed-by: Avelino <t@avelino.xxx>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>