iOS 14 - cameras don't refresh the picture in Homekit
<!-- You must use the issue template below -->

**Describe The Problem:**


**To Reproduce:**
If you run Homekit on iPhone/iPad and use Cameras menu, there are cameras, but don't refresh automatically the picture (have defined stillImageSource). On iOS 13 everything works perfectly.

**Homebridge Config:**
Standard config for cams, as I wrote, on iOS 13 everything works perfectly. For example one of my cam:
```
                {
                    "name": "XXXX",
                    "manufacturer": "Hikvision",
                    "model": "XXXX",
                    "serialNumber": "XXXX",
                    "firmwareRevision": "5.6.5",
                    "videoConfig": {
                        "source": "-rtsp_transport tcp -re -i rtsp://XXXX/Streaming/Channels/502",
                        "stillImageSource": "-i http://XXXX/ISAPI/Streaming/channels/502/picture",
                        "maxStreams": 2,
                        "maxWidth": 1280,
                        "maxHeight": 1024,
                        "maxFPS": 20
                    }
                },

```

**Environment:**

* **Node.js Version**:  12.18.3
* **NPM Version**:  6.14.6
* **Homebridge Version**: 1.2.3
* **Homebridge Camera FFmpeg Version**: 3.0.3
* **Homebridge Config UI X Plugin Version**: 4.27.1
* **Operating System**: <!-- Raspbian / Ubuntu / Debian / Windows / macOS / Docker --> Raspbian with Docker


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