Update copyright headers

authorize/authorize.go

authorize/authorize_test.go

backup/backup.go

backup/backup_test.go

backup/crypto.go

backup/crypto_test.go

backup/key.go

backup/key_test.go

backup/params.go

backup/params_test.go

broadcast/asymmetric.go

broadcast/asymmetric_test.go

broadcast/channel.go

broadcast/channel_test.go

broadcast/mac.go

broadcast/mac_test.go

broadcast/messageKey.go

broadcast/messageKey_test.go

broadcast/nonce.go

broadcast/nonce_test.go