Status not correct when sleeping
### Backstory
Status not correct when asleep and wake not working

### Issue
I can successfully switch off my mac but not waking up.
Also, the switch turns off, but after a couple of seconds the status is on again even thought the mac is still sleeping.

If i run the wakeCommand from the terminal the mac wakes up correctly.

### Configuration
My configuration looks like this:
```
{
            "accessory": "NetworkDevice",
            "name": "Macbook Pro",
            "mac": <mac-address>,
            "ip": "192.168.0.100",
            "pingInterval": 20,
            "wakeGraceTime": 10,
            "wakeCommand": "ssh user@192.168.0.100 caffeinate -u -t 300",
            "shutdownGraceTime": 15,
            "shutdownCommand": "ssh user@192.168.0.100 pmset sleepnow"
 },
```

### Environment
* os & os version: Raspbian GNU/Linux 9
* node version: v8.11.3
* homebridge version: v0.4.44
* homebridge-wol version: v3.2.4

### Log

```
Jul 26 19:57:37 pi homebridge[419]: [2018-7-26 19:57:37] [Macbook Pro] NetworkDevice shutdown cycle started for "Macbook Pro" (192.168.0.100)
Jul 26 19:57:37 pi homebridge[419]: [2018-7-26 19:57:37] [Macbook Pro] Attempting to shut down "Macbook Pro" (192.168.0.100) using "ssh user@192.168.0.100 pmset sleepnow"
Jul 26 19:57:37 pi homebridge[419]: [2018-7-26 19:57:37] [Macbook Pro] NetworkDevice "Macbook Pro" (192.168.0.100) went from status "Online" to "Shutting Down"
Jul 26 19:57:52 pi homebridge[419]: [2018-7-26 19:57:52] [Macbook Pro] NetworkDevice "Macbook Pro" (192.168.0.100) went from status "Shutting Down" to "Online"
```