MQTT options are not set for MQTT client
The quote from the main page:

> Everything set in mqtt will be passed to the options argument on Client.

It is not true according to this piece of code.

```
  publishValueToMQTT(topic, value) {
    this.mqttClient.publish(topic, String(value), {
      qos: this.config.mqtt.qos || 0
    });
  }

```
Only qos is set.
My config has
```

 "accessories": [
     {
       "mqtt": {
         "url": "mqtt://mybroker",
         "temperatureTopic": "hello/world",
         "retain": true
       },
       "accessory": "Hygrotermograph",
       "name": "Temperature & Humidity",
       "address": "MAC address",
       "timeout": 15,
       "temperatureName": "Temperature",
       "humidityName": "Humidity",
       "fakeGatoEnabled": true
     }
   ]

```
And there is no retained messages in my broker
Only with

```
    this.mqttClient.publish(topic, String(value), {
       qos: this.config.mqtt.qos || 0,
       retain: this.config.mqtt.retain || false
     });

```
I have retained changes. 

### Expected Behavior
MQTT options from config are set.

### Current Behavior
Only qos option is set.

### Steps to Reproduce (for bugs)
1. Configure a sensor to send retained MQTT messages to a broker.
2. Configure the broker to get retained MQTT messages.
3. Send a message to the broker.
4. Check that there is no retained messages in broker's queue.

### Versions
<!-- Please run commands and include versions below. -->
- **homebridge**: `homebridge --version` 0.4.50
- **homebridge-mi-hygrothermograph**: `npm list --depth 1 --global homebridge-mi-hygrothermograph` 2.3.0
- **node**:       `node --version` 9.11.2
- **OS**:         <!-- The version and architecture of your operating system --> Raspbian buster 2019-09-26

### Configuration
<!-- If relevant, include the contents of your config.json file between the two ``` lines below.
  - Remove any sensitive information, passwords, etc.
  - If output is long:
    - Please extract only the relevant portions if possible
    - Consider creating a gist, etc
 -->
```
 "accessories": [
     {
       "mqtt": {
         "url": "mqtt://mybroker",
         "temperatureTopic": "hello/world",
         "retain": true
       },
       "accessory": "Hygrotermograph",
       "name": "Temperature & Humidity",
       "address": "MAC address",
       "timeout": 15,
       "temperatureName": "Temperature",
       "humidityName": "Humidity",
       "fakeGatoEnabled": true
     }
   ]

```

### Homebridge Log / Command Output
<!-- Paste relevant output between the two ``` lines below
  - Remove any sensitive information, passwords, etc.
  - If output is long:
    - Please extract only the relevant portions if possible
    - Consider creating a gist, etc
  - However, please include the beginning of the log where the homebridge initialization happens if possible
-->
```

```
