Fixed: monitors are not registered with servo

[NiteshKant]

The code in RefCountingMonitor was:

        if (subscriptionCount.incrementAndGet() == 0) {
            ServoUtils.registerObject(monitorId, monitor);
        }

this means subscriptionCount has to be -1 for it to register. Fixed it to:

        if (subscriptionCount.getAndIncrement() == 0) {
            ServoUtils.registerObject(monitorId, monitor);
        }

[cloudbees-pull-request-builder]

RxNetty-pull-requests #111 SUCCESS
This pull request looks good

[cloudbees-pull-request-builder]

RxNetty-pull-requests #112 FAILURE
Looks like there's a problem with this pull request