任务线程移除Jetty依赖，为后续RPC模块拆分做准备；

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

 import com.xxl.job.core.log.XxlJobFileAppender;
 import com.xxl.job.core.log.XxlJobLogger;
 import com.xxl.job.core.util.ShardingUtil;
-import org.eclipse.jetty.util.ConcurrentHashSet;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.io.PrintWriter;
 import java.io.StringWriter;
+import java.util.Collections;
 import java.util.Date;
+import java.util.HashSet;
+import java.util.Set;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.TimeUnit;
 
 	private int jobId;
 	private IJobHandler handler;
 	private LinkedBlockingQueue<TriggerParam> triggerQueue;
-	private ConcurrentHashSet<Integer> triggerLogIdSet;		// avoid repeat trigger for the same TRIGGER_LOG_ID
+	private Set<Integer> triggerLogIdSet;		// avoid repeat trigger for the same TRIGGER_LOG_ID
 
 	private volatile boolean toStop = false;
 	private String stopReason;
 		this.jobId = jobId;
 		this.handler = handler;
 		this.triggerQueue = new LinkedBlockingQueue<TriggerParam>();
-		this.triggerLogIdSet = new ConcurrentHashSet<Integer>();
+		this.triggerLogIdSet = Collections.synchronizedSet(new HashSet<Integer>());
 	}
 	public IJobHandler getHandler() {
 		return handler;