Raw Socket initializing error
Hi there!
I've installed the homebridge-wol plugin like described in the instructions. 
I've also added the entry to the config.json like this:

```
{
    "accessory": "Computer",
    "name": "Boston2",
    "mac": "MY_MAC_ADDRESS",
    "ip": "192.168.178.12",
    "pingInterval": 20, 
    "wakeGraceTime": 60,
    "shutdownGraceTime": 15
},
```

Unfortunately I'm getting this error, when starting homebridge with:
`hombridge`

```
[Tue May 10 2016 19:05:19 GMT+0000 (UTC)] [Boston2] Initializing Computer accessory...
/usr/local/lib/node_modules/homebridge-wol/node_modules/net-ping/node_modules/raw-socket/index.js:47
    this.wrap = new raw.SocketWrap (
                ^

Error: Operation not permitted
    at Error (native)
    at new Socket (/usr/local/lib/node_modules/homebridge-wol/node_modules/net-ping/node_modules/raw-socket/index.js:47:14)
    at Object.exports.createSocket (/usr/local/lib/node_modules/homebridge-wol/node_modules/net-ping/node_modules/raw-socket/index.js:202:9)
    at Session.getSocket (/usr/local/lib/node_modules/homebridge-wol/node_modules/net-ping/index.js:147:20)
    at new Session (/usr/local/lib/node_modules/homebridge-wol/node_modules/net-ping/index.js:101:7)
    at Object.exports.createSession (/usr/local/lib/node_modules/homebridge-wol/node_modules/net-ping/index.js:545:9)
    at new Pinger (/usr/local/lib/node_modules/homebridge-wol/index.js:114:24)
    at new Computer (/usr/local/lib/node_modules/homebridge-wol/index.js:28:16)
    at Server._loadAccessories (/usr/local/lib/node_modules/homebridge/lib/server.js:244:29)
    at Server.run (/usr/local/lib/node_modules/homebridge/lib/server.js:72:38)
```

All my other plugins are setting up correctly except the wol alias Computer plugin. 
It seems for me like an issue in the raw-socket module but I just want to make sure I didn't misconfigured anything.

Thanks in advance!
