title: Shedlock has run duplicate when run multi instance
body: <p>I am using shedlock to make sure only 1 Schedule Task can run at same time when I have multi instances</p>
  
  <pre><code>&lt;dependency&gt;
          &lt;groupId&gt;net.javacrumbs.shedlock&lt;/groupId&gt;
          &lt;artifactId&gt;shedlock-spring&lt;/artifactId&gt;
          &lt;version&gt;4.5.2&lt;/version&gt;
      &lt;/dependency&gt;
      &lt;dependency&gt;
          &lt;groupId&gt;net.javacrumbs.shedlock&lt;/groupId&gt;
          &lt;artifactId&gt;shedlock-provider-jdbc-template&lt;/artifactId&gt;
          &lt;version&gt;4.6.0&lt;/version&gt;
      &lt;/dependency&gt;
  
  @Configuration
  @EnableScheduling
  @EnableSchedulerLock(
  defaultLockAtMostFor = "${scheduled.task.lock.at.most}", 
  defaultLockAtLeastFor = "${scheduled.task.lock.at.least}")
  public class SchedulerConfig implements AsyncConfigurer, SchedulingConfigurer {
  
  @Override
  public void configureTasks(ScheduledTaskRegistrar taskRegistrar) {
      // TODO Auto-generated method stub
      TaskScheduler scheduler = this.taskScheduler();
      taskRegistrar.setTaskScheduler(scheduler);
  }
  
  @Override
  public Executor getAsyncExecutor() {
      Executor executor = this.taskScheduler();
      return executor;
  }
  
  // shedlock config
  @Bean
  public LockProvider lockProvider(DataSource dataSource) {
      return new JdbcTemplateLockProvider(dataSource);
  }  
  }
  </code></pre>
  
  <p>Here is my task</p>
  
  <pre><code>@Scheduled(cron = "0 36 16 * * ?") //
   @net.javacrumbs.shedlock.spring.annotation.SchedulerLock(name = "ms.template.scheduleTaskJob2")
  public void scheduleTaskJob2() {
      // Mandatory information for logging
      String _id = "schedule-" + UUID.randomUUID().toString();
      ThreadContext.put("serviceMessageId", _id);
  
      logger.info("Cron Expression task called at the 0 second every minutes Execution Time - {}",
              dateTimeFormatter.format(LocalDateTime.now()));
  }
  </code></pre>
  
  <p>But in both 2 instance of my app, the schedule task is execute, and This info is show in DB</p>
  
  <pre><code>ms.template.scheduleTaskJob2    26-MAR-20 04.51.00.001824000 PM 26-MAR-20 04.36.00.392858000 PM MB0001-PCHOBW41
  ms.template.scheduleTaskJob2    26-MAR-20 04.51.00.004479000 PM 26-MAR-20 04.36.00.298564000 PM MB0001-PCHOBT97
  </code></pre>
  
  <p>Why this error is occur?
  Many thank!</p>