modify reference

Author: Pliza

docs/high-availability/hystrix-circuit-breaker.md

@@ -197,5 +197,4 @@ ProductInfo(id=1, name=iphone7手机, price=5599.0, pictureList=a.jpg,b.jpg, spe
 ### 参考内容
 
 1. [Hystrix issue 1459](https://github.com/Netflix/Hystrix/issues/1459)
-2. [Hystrix Metrics](https://github.com/Netflix/Hystrix/wiki/Configuration#metrics)
-3. 
+2. [Hystrix Metrics](https://github.com/Netflix/Hystrix/wiki/Configuration#metrics)