Not waking/shutting down my iMac
### Backstory
Using the plugin via the Home App

### Issue
I successfully installed homebridge-wol and added the configuration to the config file. The plugin seems to be running fine and my iMac 5K shows up in HomeKit. 

However, I am not not able to either wake up or shut down my computer. Nor does the plugin update my iMac status if I manually turn it on or off. The switch doesn't seem to do anything.

Here is screenshots of my networking settings:

<img width="780" alt="screen shot 2018-01-31 at 1 16 53 pm" src="https://user-images.githubusercontent.com/25128243/35647953-0ce91d64-0689-11e8-9097-39f08a0426a9.png">
<img width="780" alt="screen shot 2018-01-31 at 1 17 00 pm" src="https://user-images.githubusercontent.com/25128243/35647954-0d04014c-0689-11e8-87a9-694f9bd6ba25.png">

And here is my configuration file:

```
{
    "bridge": {
        "name": "Homebridge Misc",
        "username": "CD:22:4D:E3:DE:34",
        "port": 51826,
        "pin": "051-85-128"
    },
    "description": "This is an example configuration file. You can use this as a template for creating your own configuration file containing devices you actually own.",
    "accessories": [
        {
            "accessory": "NetworkDevice",
            "name": "iMac 5k",
            "mac": "<mac-address>",
            "ip": "10.0.1.12",
            "pingInterval": 45,
            "wakeGraceTime": 90,
            "shutdownGraceTime": 45,
            "shutdownCommand": "ssh 10.0.1.12 sudo shutdown -h now"
        }
    ],
    "platforms": [
        {
            "platform": "config",
            "name": "Config",
            "port": 8170,
            "log": "/homebridge/logs/homebridge.log",
            "restart": "docker-compose restart homebridge"
        }
    ]
}
```


### Environment
* os & os version: Raspberry Pi 3 - Raspian OS
* node version: not sure
* homebridge version: 0.4.37 (running via OZNU Docker)
* homebridge-wol version: 3.1.0

### Log
When I follow these steps:
I couldn't figure out how to run the  `DEBUG=* homebridge` command. However, here is a copy of my log file:

I get the following log:
```
[2018-1-31 13:02:22] Homebridge is running on port 51826.
[2018-1-31 13:02:25] [Config] Using Form Authentication
[2018-1-31 13:02:25] [Config] Console is listening on port 8170.
[2018-1-31 13:03:55] [Config] Changes to config.json saved.

/usr/local/lib/node_modules/homebridge/node_modules/mdns/lib/advertisement.js:42
    var error = dns_sd.buildException(errorCode);
                       ^
Error: dns service error: unknown
    at Advertisement.on_service_registered (/usr/local/lib/node_modules/homebridge/node_modules/mdns/lib/advertisement.js:42:24)
    at SocketWatcher.MDNSService.self.watcher.callback (/usr/local/lib/node_modules/homebridge/node_modules/mdns/lib/mdns_service.js:18:40)
*** WARNING *** The program 'node' uses the Apple Bonjour compatibility layer of Avahi.
*** WARNING *** Please fix your application to use the native API of Avahi!
*** WARNING *** For more information see <http://0pointer.de/avahi-compat?s=libdns_sd&e=node>
*** WARNING *** The program 'node' called 'DNSServiceRegister()' which is not supported (or only supported partially) in the Apple Bonjour compatibility layer of Avahi.
*** WARNING *** Please fix your application to use the native API of Avahi!
*** WARNING *** For more information see <http://0pointer.de/avahi-compat?s=libdns_sd&e=node&f=DNSServiceRegister>
[2018-1-31 13:04:30] Loaded plugin: homebridge-dummy
[2018-1-31 13:04:30] Registering accessory 'homebridge-dummy.DummySwitch'
[2018-1-31 13:04:30] ---
[2018-1-31 13:04:30] Loaded plugin: homebridge-wol
[2018-1-31 13:04:30] Registering accessory 'homebridge-wol.NetworkDevice'
[2018-1-31 13:04:30] ---
[2018-1-31 13:04:31] Loaded plugin: homebridge-config-ui-x
[2018-1-31 13:04:31] Registering platform 'homebridge-config-ui-x.config'
[2018-1-31 13:04:31] ---
[2018-1-31 13:04:31] Loaded config.json with 1 accessories and 1 platforms.
[2018-1-31 13:04:31] ---
[2018-1-31 13:04:31] Loading 1 platforms...
[2018-1-31 13:04:31] [Config] Initializing config platform...
[2018-1-31 13:04:31] Loading 1 accessories...
[2018-1-31 13:04:31] [iMac 5k] Initializing NetworkDevice accessory...
Setup Payload:
X-HM://0023K0OYWKCPC
Scan this code with your HomeKit app on your iOS device to pair with Homebridge:



























Or enter this code with your HomeKit app on your iOS device to pair with Homebridge:

    ┌────────────┐
    │ 051-85-128 │
    └────────────┘

[2018-1-31 13:04:31] Homebridge is running on port 51826.
[2018-1-31 13:04:34] [Config] Using Form Authentication
[2018-1-31 13:04:34] [Config] Console is listening on port 8170.
[2018-1-31 13:07:39] [iMac 5k] NetworkDevice awake cycle started for "iMac 5k" (10.0.1.12)
[2018-1-31 13:07:39] [iMac 5k] Attempting to wake up "iMac 5k" (10.0.1.12)
[2018-1-31 13:07:39] [iMac 5k] NetworkDevice "iMac 5k" (10.0.1.12) went from status "Offline" to "Waking Up"
[2018-1-31 13:07:44] [iMac 5k] NetworkDevice shutdown cycle started for "iMac 5k" (10.0.1.12)
[2018-1-31 13:07:44] [iMac 5k] Attempting to shut down "iMac 5k" (10.0.1.12) using "ssh 10.0.1.12 sudo shutdown -h now"
[2018-1-31 13:07:44] [iMac 5k] NetworkDevice "iMac 5k" (10.0.1.12) went from status "Waking Up" to "Shutting Down"
[2018-1-31 13:07:44] [iMac 5k] An error occured while trying to shut down "iMac 5k" (10.0.1.12): Error: Command failed: ssh 10.0.1.12 sudo shutdown -h now
/bin/sh: ssh: not found

[2018-1-31 13:07:44] [iMac 5k] NetworkDevice "iMac 5k" (10.0.1.12) went from status "Shutting Down" to "Offline"
[2018-1-31 13:10:21] [iMac 5k] NetworkDevice awake cycle started for "iMac 5k" (10.0.1.12)
[2018-1-31 13:10:21] [iMac 5k] Attempting to wake up "iMac 5k" (10.0.1.12)
[2018-1-31 13:10:21] [iMac 5k] NetworkDevice "iMac 5k" (10.0.1.12) went from status "Offline" to "Waking Up"
[2018-1-31 13:11:51] [iMac 5k] NetworkDevice "iMac 5k" (10.0.1.12) went from status "Waking Up" to "Offline"
```

### Notes
I would love to get your help with this problem. I was REALLY excited to be able to remotely turn off and turn on my iMac. Please let me know if there is any additional information you need from me!