An error occured while trying to start the device (5.0.0-Beta1)
### Backstory
I tried installing Beta5.0 after I was only able to run wol/suspend once in v4.3.0 before it hangs and requiring a restart to homebridge to restore functionality.

### Issue
In Beta5.0 issue seems the above issue is resolved, however I get this weird prompt in the logs '[NetworkDevice] An error occured while trying to shut down the device'. From the little testing I've done, it does not seem to break functionality at all.

### Environment
* os & os version: Buster
* node version: 14.15.5
* homebridge version: 1.3.0-beta58
* homebridge-wol version: v5.0.0-beta1

### Configuration
My configuration looks like this:
```
        {
            "name": "Washroom Computer",
            "manufacturer": "homebridge-wol",
            "model": "Family Computer",
            "host": "192.168.1.3",
            "pingInterval": 2,
            "pingsToChange": 5,
            "pingTimeout": 1,
            "pingCommandTimeout": 0,
            "mac": "<mac-address>",
            "startCommand": "Wol://<mac-address>",
            "startCommandTimeout": 1,
            "wakeGraceTime": 20,
            "wakeCommandTimeout": 0,
            "shutdownCommand": "ssh -o StrictHostKeyChecking=no -i /home/homebridge/computer/id_rsa \"Family Computer\"@192.168.1.3 shutdown /h",
            "shutdownGraceTime": 30,
            "shutdownCommandTimeout": 1,
            "logLevel": "Info",
            "returnEarly": true,
            "accessory": "NetworkDevice"
        },
        {
            "name": "Mark's Room Workstation",
            "manufacturer": "homebridge-wol",
            "model": "Mark's Workstation",
            "host": "192.168.1.2",
            "pingInterval": 2,
            "pingsToChange": 5,
            "pingTimeout": 1,
            "pingCommandTimeout": 1,
            "mac": "<mac-address>",
            "startCommand": "Wol://<mac-address>",
            "startCommandTimeout": 0,
            "wakeGraceTime": 50,
            "wakeCommandTimeout": 0,
            "shutdownCommand": "ssh -o StrictHostKeyChecking=no -i /home/homebridge/workstation/id_rsa \"Mark's Workstation\"@192.168.1.2 shutdown /h",
            "shutdownGraceTime": 50,
            "shutdownCommandTimeout": 1,
            "logLevel": "Info",
            "returnEarly": true,
            "accessory": "NetworkDevice"
        }
```

### Log

2/17/2021 12:40:41] [Washroom Computer] [NetworkDevice] Device went from status "Offline" to "Online"
[2/17/2021 12:40:56] [Washroom Computer] [NetworkDevice] Shutdown cycle started
[2/17/2021 12:40:56] [Washroom Computer] [NetworkDevice] Device went from status "Online" to "ShuttingDown"
[2/17/2021 12:40:56] [Washroom Computer] [NetworkDevice] Attempting to shut down the device using "ssh"
[2/17/2021 12:40:57] [Washroom Computer] [NetworkDevice] An error occured while trying to shut down the device
[2/17/2021 12:40:57] [Washroom Computer] [NetworkDevice] Waiting for shutdown grace time (NaNms)
[2/17/2021 12:41:28] [Washroom Computer] [NetworkDevice] Device went from status "ShuttingDown" to "Offline"
[2/17/2021 12:41:30] [Washroom Computer] [NetworkDevice] Awake cycle started
[2/17/2021 12:41:30] [Washroom Computer] [NetworkDevice] Attempting to wake up device
[2/17/2021 12:41:30] [Washroom Computer] [NetworkDevice] Device went from status "Offline" to "WakingUp"
[2/17/2021 12:41:30] [Washroom Computer] [NetworkDevice] Waiting for wake grace time (20000ms)
[2/17/2021 12:41:50] [Washroom Computer] [NetworkDevice] Device went from status "WakingUp" to "Online"
[2/17/2021 12:41:54] [Washroom Computer] [NetworkDevice] Shutdown cycle started
[2/17/2021 12:41:54] [Washroom Computer] [NetworkDevice] Device went from status "Online" to "ShuttingDown"
[2/17/2021 12:41:54] [Washroom Computer] [NetworkDevice] Attempting to shut down the device using "ssh"
[2/17/2021 12:41:55] [Washroom Computer] [NetworkDevice] An error occured while trying to shut down the device
[2/17/2021 12:41:55] [Washroom Computer] [NetworkDevice] Waiting for shutdown grace time (NaNms)
[2/17/2021 12:42:26] [Washroom Computer] [NetworkDevice] Device went from status "ShuttingDown" to "Offline"
