ChunkRunner spawning a thousands of chunk-checkpoint-timer threads

As described in the pull request 120 I copy the description body:

Hi,
today I found that if time-limit was set to a big number of seconds my JVM struggled keeping track of thousands of threads named chunk-checkpoint-timer on certain job.

Investigating on the source code I found that org.jberet.runtime.runner.ChunkRunner class, when time-limit attribute on chunk tag was set bigger than 0, scheduled a timed thread just to update a boolean flag

            if (timeLimit > 0) {
                final Timer timer = new Timer("chunk-checkpoint-timer", true);
                timer.schedule(new TimerTask() {
                    @Override
                    public void run() {
                        processingInfo.timerExpired = true;
                    }
                }, timeLimit * 1000);
            }

I don't know if can be an intended behavior, but java.util.Timer class was not officially but practically deprecated in favor of java.util.concurrent.ScheduledThreadPoolExecutor. In any case here I tried to totally bypass the usage of threads and checking the expiration of the chunk only with a simpler check on the current millis with System.currentTimeMillis().