timingwheel.go:(TimingWheel)After()函数中index计算不正确

[AlexStocks]

siddontang，在查看你的时间轮代码时候，觉得(TimingWheel)After()函数中index计算不正确，为了验证猜想，我写了如下测试用例：

• https://github.com/AlexStocks/go-practice/blob/master/time/siddontang_time_wheel.go

输出是：expect time cost 100s, while real time cost is 110 s.
显然，当运行次数越多，你的timingwheel的时间误差将越多，我给你修正后的(TimingWheel)After()函数代码如下：
func (w *TimingWheel) After(timeout time.Duration) <-chan struct{} {
if timeout >= w.maxTimeout {
panic("timeout too much, over maxtimeout")
}

index := int(timeout / w.interval)
if 0 < index {
    index--
}
w.Lock()

index = (w.pos + index) % len(w.cs)

b := w.cs[index]

w.Unlock()

return b

}

再次运行我的测试用例后，输出如下：
expect time cost 100s, while real time cost is 100 s.

This output is perfect.