!322 Cron表达式生成器关闭时销毁，避免再次打开时存在上一次修改的数据

Merge pull request !322 from muyi/master

ruoyi-ui/src/views/monitor/job/index.vue

@@ -240,7 +240,7 @@
       </div>
     </el-dialog>
 
-    <el-dialog title="Cron表达式生成器" :visible.sync="openCron" append-to-body class="scrollbar">
+    <el-dialog title="Cron表达式生成器" :visible.sync="openCron" append-to-body class="scrollbar"  destroy-on-close >
       <crontab @hide="openCron=false" @fill="crontabFill" :expression="expression"></crontab>
     </el-dialog>