🚀 Update cpuUsage code

Author: aozhimin

README.md

@@ -381,16 +381,15 @@ static NSUInteger const kMaxPercent = 100;
  return -1;
  }
  
- natural_t user = info.cpu_ticks[CPU_STATE_USER] + info.cpu_ticks[CPU_STATE_NICE]
-    - previous_info.cpu_ticks[CPU_STATE_USER] - previous_info.cpu_ticks[CPU_STATE_NICE];
+ natural_t user = info.cpu_ticks[CPU_STATE_USER] - previous_info.cpu_ticks[CPU_STATE_USER];
+ natural_t nice = info.cpu_ticks[CPU_STATE_NICE] - previous_info.cpu_ticks[CPU_STATE_NICE];
  natural_t system = info.cpu_ticks[CPU_STATE_SYSTEM] - previous_info.cpu_ticks[CPU_STATE_SYSTEM];
  natural_t idle = info.cpu_ticks[CPU_STATE_IDLE] - previous_info.cpu_ticks[CPU_STATE_IDLE];
- natural_t total = user + system + idle;
+ natural_t total = user + nice + system + idle;
  previous_info = info;
  
- return (user + system) * 100.0 / total;
+ return (user + nice + system) * 100.0 / total;
 }
-
 ```
 
 上面代码通过计算 `info` 和 `previous_info` 的差值，分别得到在这几个模式下的 `cpu_ticks`，除 `idle` 以外都属于 CPU 被占用的情况，最后就能求出 CPU 的占用率。