fix typo in thread command description (alibaba#2690)

Author: obslayer

core/src/main/java/com/taobao/arthas/core/command/monitor200/ThreadCommand.java

@@ -96,7 +96,7 @@ public void setSampleInterval(int sampleInterval) {
     }
 
     @Option(longName = "state")
-    @Description("Display the thead filter by the state. NEW, RUNNABLE, TIMED_WAITING, WAITING, BLOCKED, TERMINATED is optional.")
+    @Description("Display the thread filter by the state. NEW, RUNNABLE, TIMED_WAITING, WAITING, BLOCKED, TERMINATED is optional.")
     public void setState(String state) {
         this.state = state;
     }
@@ -238,4 +238,4 @@ private ExitStatus processThread(CommandProcess process) {
         process.appendResult(new ThreadModel(threadInfos[0]));
         return ExitStatus.success();
     }
-}
+}