add a quick benchmark to transformOne

[nstott]

nothing much to see here

$ go test ./... -bench .
?       github.com/compose/transporter/cmd/transporter  [no test files]
PASS
BenchmarkTransformOne     100000         18766 ns/op
ok      github.com/compose/transporter/pkg/adaptor  2.208s
PASS
ok      github.com/compose/transporter/pkg/events   0.007s
PASS
ok      github.com/compose/transporter/pkg/message  0.004s
?       github.com/compose/transporter/pkg/pipe [no test files]
PASS
ok      github.com/compose/transporter/pkg/transporter  0.008s

[jipperinbham]

👍