The case BenchmarkRange seems has some problem ? #10

// syncmap code:
	b.Run(fmt.Sprintf("%T", &IntMap{}), func(b *testing.B) {
		m := &IntMap{}
		// setup:

		// reset:
		b.ResetTimer()

		// perG:
		perG := func(b *testing.B, pb *testing.PB, i int, m *IntMap) {
			for ; pb.Next(); i++ {
				m.Range(func(_, _ int) bool { return true })
			}
		}
		var i int64
		b.RunParallel(func(pb *testing.PB) {
			id := int(atomic.AddInt64(&i, 1) - 1)
			perG(b, pb, id*b.N, m)
		})
	})