serialNumber does not work in Eve
**Describe the bug**
I set `serialNumber`. It does show up in in Home but it does not show up in Eve.


**Expected behavior**
I would expect the serial number to appear in both apps. 

**To Reproduce**
Steps to reproduce the behavior:
1. Edit config.json as shown

        {
            "accessory": "HTTP-SWITCH",
            "name": "Arming error",
            "switchType": "stateless",
            "serialNumber": "SW003",
            "timeout": 1000,
            "onUrl": "https://maker.ifttt.com/t...",
            "method": "POST",
            "debug": false
        },

2. Restarthomebridge
3. Check Eve
4. Check Home

**Version** (output of `npm list -g homebridge homebridge-http-switch`)
 - homebridge: 1.1.1
 - homebridge-http-switch: v0.5.31

**Configuration**
```json
....
```

**Additional context**
Add any other context about the problem here.
