minBitrate seems to not work
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**Describe The Bug:**
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The stream seems to default to 299 Kbit/s regardless of what's set in `minBitrate`.

This issue has cropped up in the last few versions of this plugin. 

**To Reproduce:**
Set `minBitrate` and restart HB. 

**Expected behavior:**
The video stream should be in the minimum quality as configured. 

**Logs:**
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```text
[7/15/2020, 7:49:20 PM] [Camera ffmpeg] Starting Front Gate CCTV video stream (1280x720, 20 fps, 299 kbps, 1316 mtu)...
```

**Homebridge Config:**

```json
{
                    "name": "Front Gate CCTV",
                    "manufacturer": "D-Link",
                    "model": "DCS-933L",
                    "firmwareRevision": "1.15.01",
                    "motion": false,
                    "videoConfig": {
                        "source": "-re -f mjpeg -i http://admin:password@10.0.0.6/mjpeg.cgi",
                        "stillImageSource": "-f mjpeg -i http://admin:password@10.0.0.6/image.jpg",
                        "maxStreams": 2,
                        "maxWidth": 1280,
                        "maxHeight": 720,
                        "maxFPS": 20,
                        "minBitrate": 7500,
                        "maxBitrate": 7501,
                        "videoFilter": "scale=640:480",
                        "vcodec": "libx264",
                        "audio": false,
                        "debug": false
                    }
```

**Screenshots:**
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**Environment:**

* **Node.js Version**: 12.18.2
* **NPM Version**: 6.14.5
* **Homebridge Version**: 1.1.1
* **Homebridge Camera FFmpeg Version**: 2.3.0
* **Homebridge Config UI X Plugin Version**:
* **Operating System**: Raspberry Pi OS Buster


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