update doc

xxl-job-core/src/main/java/com/xxl/job/core/constant/Const.java

@@ -25,4 +25,12 @@ public class Const {
      */
     public static final int DEAD_TIMEOUT = BEAT_TIMEOUT * 3;
 
+
+    // ---------------------- for executor ----------------------
+
+    /*
+     * elegant shutdown wait seconds
+     */
+    public static final long ELEGANT_SHUTDOWN_WAITING_SECONDS = 5;
+
 }

xxl-job-core/src/main/java/com/xxl/job/core/context/XxlJobContext.java

@@ -138,7 +138,7 @@ public class XxlJobContext {
     /**
      * xxl-job context store
      */
-    private static final InheritableThreadLocal<XxlJobContext> contextHolder = new InheritableThreadLocal<XxlJobContext>(); // support for child thread of job handler)
+    private static final InheritableThreadLocal<XxlJobContext> contextHolder = new InheritableThreadLocal<>(); // support for child thread of job handler)
 
     /**
      * set xxl-job context