fix: sys.timerLoopStart中,timer id的变量作用域问题

luat/modules/luat_lib_sys_doc.c

@@ -91,7 +91,8 @@ void doc_sys_timerLoopStart(void){};
 @return nil 无返回值
 @usage
 local tcount = 0
-local tid = sys.timerLoopStart(function(a, b, c)
+local tid 
+tid = sys.timerLoopStart(function(a, b, c)
     log.info("task", a, b, c) -- 1000毫秒后才会执行, 打印 task A B C
     if tcount > 10 then
         sys.timerStop(tid)