任务线程停止变量修饰符优化

doc/XXL-JOB官方文档.md

 - 10、底层LocalCache组件兼容性优化，支持jdk、jdk10编译部署；
 - 11、任务回调结果优化，支持展示在Rolling log中，方便问题排查；
 - 12、脚本任务异常Log输出优化；
+- 13、任务线程停止变量修饰符优化；
 
 
 ### TODO LIST

xxl-job-core/src/main/java/com/xxl/job/core/thread/JobThread.java

 	private LinkedBlockingQueue<TriggerParam> triggerQueue;
 	private ConcurrentHashSet<Integer> triggerLogIdSet;		// avoid repeat trigger for the same TRIGGER_LOG_ID
 
-	private boolean toStop = false;
+	private volatile boolean toStop = false;
 	private String stopReason;
 
     private boolean running = false;    // if running job