Logger is slow in OFF level

[vicanso]

I set the log's level to OFF and I thought that log function should be fast. However it seemed to be slower than of noop function. I have tested like this:

func BenchmarkEchoLog(b *testing.B) {
    e := echo.New()
    e.Logger.SetLevel(log.Lvl(log.OFF))
    c := e.NewContext(nil, nil)
    for i := 0; i < b.N; i++ {
        c.Logger().Debug("a")
    }
}

func BenchmarkNoop(b *testing.B) {
    noop := func(args ...interface{}) {}
    for i := 0; i < b.N; i++ {
        noop("a")
    }
}

BenchmarkEchoLog-4                       1000000          1778 ns/op
BenchmarkNoop-4                         30000000            40.8 ns/op