JSON syntax error in GUI with default config
<!-- If you have an issue with a plugin create an issue on that plugin's GitHub page instead. -->

<!-- Before opening an issue, please review the Troubleshooting Page on the Wiki to ensure that this is a new issue, and alternatively search the closed issues for similar problems. -->

<!-- Link to the the Wiki - https://github.com/nfarina/homebridge/wiki -->

<!-- Provide a general summary in the Title above -->

**Describe The Bug:**
When trying to save the default config through the web GUI, an error notification appears, telling me that the JSON has an invalid syntax even though it is the default config that comes with installiation. Any JSON validator tells me that this is valid JSON.
```json
{
    "bridge": {
        "name": "Homebridge REDACTED",
        "username": "AA:AA:AA:AA:AA:AA",
        "port": 51927,
        "pin": "111-11-111"
    },
    "accessories": [],
    "platforms": [
        {
            "name": "Config",
            "port": 8581,
            "platform": "config"
        }
    ]
}
```
<!-- A clear and concise description of what the bug is. -->

**To Reproduce:**
1. Open Homebridge GUI
2. Open /config
3. Save
<!-- Steps to reproduce the behavior. -->

**Expected behavior:**
The GUI tells me that the config file could have been saved succesfully.
<!-- A clear and concise description of what you expected to happen. -->


**Homebridge Config:**
<!-- Paste relevant output between the two ``` lines below -->
<!-- Remove any sensitive information, passwords, etc. -->

```json
{
    "bridge": {
        "name": "Homebridge REDACTED",
        "username": "AA:AA:AA:AA:AA:AA",
        "port": 51927,
        "pin": "111-11-111"
    },
    "accessories": [],
    "platforms": [
        {
            "name": "Config",
            "port": 8581,
            "platform": "config"
        }
    ]
}
```

**Screenshots:**
<!-- If applicable, add screenshots to help explain your problem. -->
<img width="912" alt="Bildschirmfoto 2021-02-07 um 14 02 32" src="https://user-images.githubusercontent.com/66573402/107147214-23442980-694d-11eb-982f-5163bf7b944b.png">

**Environment:**

* **Node.js Version**: <!-- node -v --> 14.15.4
* **NPM Version**: <!-- npm -v --> 7.5.2
* **Homebridge Version**: <!-- homebridge -V --> 1.1.7
* **Operating System**: Raspbian 
* **Process Supervisor**: Systemd / init.d / pm2 / launchctl / Docker / hb-service / other / none

<!-- Click the "Preview" tab before you submit to ensure the formatting is correct. -->
