Fixed: monitors are not registered with servo

The code in `RefCountingMonitor` was:

```java
        if (subscriptionCount.incrementAndGet() == 0) {
            ServoUtils.registerObject(monitorId, monitor);
        }
```

this means subscriptionCount has to be -1 for it to register. Fixed it to:

```java
        if (subscriptionCount.getAndIncrement() == 0) {
            ServoUtils.registerObject(monitorId, monitor);
        }
```