注释里的时间单位typo: "纳秒" -> "微秒"

[KathyW666]

_timeval.h 中 tv_usec 为 microseconds
https://opensource.apple.com/source/xnu/xnu-6153.41.3/bsd/sys/_types/_timeval.h.auto.html

Issue line:

TimeProfiler/TimeProfiler/Core/TPCallTrace.h

Line 19 in ca27741

uint64_t costTime; //单位：纳秒（百万分之一秒）

TimeProfiler/TimeProfiler/Core/TPCallTrace.c

Line 72 in ca27741

uint64_t time = (now.tv_sec % 1000) * 1000000 + now.tv_usec;