SyntaxError: Block-scoped ... strict mode.
### Backstory
I was attempting to re-configure homebridge-wol due to a recent move w/ switch of equipment.

### Issue
I do not know what exactly happened, it didn't yell at me before. I've updated and reinstalled everything (including deleting the .homebridge folder at ~/ and /root/) to make sure something didn't corrupt or anything.

### Environment
- [ x] * Os & os version: Raspbian 9 stretch  | Controlling a Windows 10.pre.1803 desktop
- [ x] * node version: 4.8.2
- [ x] * homebridge version: 4.38
- [ x] * homebridge-wol version: 3.2.2

### Configuration
My configuration looks like this:
```
{
   "bridge": {
        "name": "Homebridge",
        "username": "<Mac-address>",
        "port": 51826,
        "pin": "031-45-154"
   },
"accessories":[
   {
        "accessory": "WinPC",
        "name": "My Windows PC",
        "http_method": "GET",
        "on_url": "wol://<Mac-address>",
        "off_url": "http://10.0.0.1:7879/?action=System.Shutdown",
        "status_url": "http://10.0.0.1:7879/",
        "sendimmediately": "yes",
        "poll_status_interval": "60",
        "username" : "User",
        "password" : "<Mac-address>",
        "powerstateOnError" : "0",
        "powerstateOffError": "1"
   },
   {
       "accessory": "NetworkDevice",
       "name": "PC",
       "mac": "<Mac-address>",
       "ip": "10.0.0.1",
       "shutdownCommand": "net rpc shutdown --ipaddress 10.0.0.1 --user redacted%redacted"
   }
 ]
}
```
IMPORTANT!
- [x ] Remove any mac addresses from the configuration by 
exchanging them with <Mac-address>


### Log
Homebridge fails to load at error, so can't really debug. But, here is the console output.
```
[28/04/2018, 22:16:41] Loaded plugin: homebridge-winpc
[28/04/2018, 22:16:41] Registering accessory 'homebridge-winpc.WinPC'
[28/04/2018, 22:16:41] ---
[28/04/2018, 22:16:41] ====================
[28/04/2018, 22:16:41] ERROR LOADING PLUGIN homebridge-wol:
[28/04/2018, 22:16:41] SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode
    at exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:373:25)
    at Module.load (module.js:343:32)
    at Function.Module._load (module.js:300:12)
    at Module.require (module.js:353:17)
    at require (internal/module.js:12:17)
    at Object.<anonymous> (/usr/local/lib/node_modules/homebridge-wol/index.js:1:88)
    at Module._compile (module.js:409:26)
    at Object.Module._extensions..js (module.js:416:10)
[28/04/2018, 22:16:41] ====================
[28/04/2018, 22:16:41] Loaded config.json with 2 accessories and 0 platforms.
[28/04/2018, 22:16:41] ---
[28/04/2018, 22:16:41] Loading 2 accessories...
[28/04/2018, 22:16:41] [My Windows PC] Initializing WinPC accessory...
[28/04/2018, 22:16:41] [My Windows PC] Setting info: {"serialnumber":"Unknown","model":"Windows PC","manufacterer":"Microsoft","name":"Windows PC","softwareversion":"Unknown","manufacturer":"Microsoft"}
HAP Warning: Characteristic 00000054-0000-1000-8000-0026BB765291 not in required or optional characteristics for service 0000003E-0000-1000-8000-0026BB765291. Adding anyway.
/usr/local/lib/node_modules/homebridge/lib/api.js:64
      throw new Error("The requested accessory '" + name + "' was not registered by any plugin.");
      ^

Error: The requested accessory 'NetworkDevice' was not registered by any plugin.
    at API.accessory (/usr/local/lib/node_modules/homebridge/lib/api.js:64:13)
    at Server.str.replace.Server._loadAccessories (/usr/local/lib/node_modules/homebridge/lib/server.js:264:42)
    at Server.str.replace.Server.run (/usr/local/lib/node_modules/homebridge/lib/server.js:86:38)
    at module.exports (/usr/local/lib/node_modules/homebridge/lib/cli.js:40:10)
    at Object.<anonymous> (/usr/local/lib/node_modules/homebridge/bin/homebridge:17:22)
    at Module._compile (module.js:409:26)
    at Object.Module._extensions..js (module.js:416:10)
    at Module.load (module.js:343:32)
    at Function.Module._load (module.js:300:12)
    at Function.Module.runMain (module.js:441:10)
```
### Notes
none
