TH16 with DS18B20 temperature sensor is displaying 0% humidity value
### What issue do you have? Please be as thorough and explicit as possible.
The TH16 equipped with the sensor DS18B20 is displaying a 0% humidity value. This sensor is a temperature sensor only and _it does not measure relative humidity_. In versions of this plugin previous to 5.0.0 there was no humidity value displayed in Apple Home.


### Details of your setup.
* Do you use (1) Homebridge (+ config-ui), (2) Homebridge (CLI) or (3) HOOBS? 
(1) Homebridge (+ config-ui)


* Which version of Homebridge/HOOBS do you have?
Homebridge v1.3.4


* Which platform do you run Homebridge/HOOBS on (e.g. Raspberry Pi/Windows/HOOBS Box)? Please also mention your version of Node.js/NPM if known.
Raspbian GNU/Linux Buster (10)
Node.js Version v14.16.1
Npm Version v6.14.12


* Which version of this plugin (homebridge-ewelink) do you have? Has the issue started since upgrading from a previous version?
homebridge-ewelink v6.1.1
Issue started from v5.0.0


* Which eWeLink devices do you have that are causing issues? Please include product models if applicable.
Sonoff TH16R2 (PSA-BHA-GL) (firmware 3.4.1) + temperature sensor DS18B20


### Please paste any relevant logs below.
```
[14/04/2021, 08:24:28] [eWeLink] [v6.1.1] initialised. Syncing with eWeLink.
[14/04/2021, 08:24:29] [eWeLink] Sending HTTP login() request.
[14/04/2021, 08:24:32] [eWeLink] Web socket host received [eu-pconnect5.coolkit.cc].
[14/04/2021, 08:24:34] [eWeLink] LAN discovery starting.
[14/04/2021, 08:24:34] [eWeLink] Sending WS login request.
[14/04/2021, 08:24:34] [eWeLink] WS login successful.
[[14/04/2021, 08:24:37] [eWeLink] LAN discovery complete.
[14/04/2021, 08:24:37] [eWeLink] LAN monitoring started.
[14/04/2021, 08:24:37] [eWeLink] [Pool Temperature] initialising with options {"disableDeviceLogging":false,"hideSwitch":true,"offset":0}.
[14/04/2021, 08:24:39] [eWeLink] [Pool Temperature] initialised and found locally with IP [192.168.0.66].
[14/04/2021, 08:24:39] [eWeLink] ✓ Setup complete. Don't forget to ☆ this plugin on GitHub if you're finding it useful!
[14/04/2021, 08:28:36] [eWeLink] [Pool Temperature] receiving update {"switch":"off","sensorType":"DS18B20","humidity":0,"temperature":18.61,"online":true,"updateSource":"LAN"}.
[14/04/2021, 08:28:36] [eWeLink] [Pool Temperature] receiving update {"switch":"off","mainSwitch":"off","online":true,"updateSource":"WS"}.
```
