When the function Call sets a timeout, a coroutine will be opened internally circuitbreaker.go [line 350](https://github.com/rubyist/circuitbreaker/blob/master/circuitbreaker.go#L350) - [line 353](https://github.com/rubyist/circuitbreaker/blob/master/circuitbreaker.go#L353) Hope to provide AsyncCall , internal coroutines cannot be used
