Error with Led strip
<!-- PLEASE READ BEFORE POSTING A NEW ISSUE
   → If you are giving feedback or requesting a new feature then feel free to ignore this template.
   → If you are experiencing an issue with the plugin then please use this template as well as you can.
   → Things that may seem unimportant to you are often helpful in finding the cause of the issue.
-->

### What issue do you have? Please be as thorough and explicit as possible.
Since version 6.1.0 of the plugin, I have an error with sonof led strip


### Details of your setup.
* Do you use Homebridge (with config-ui?) or HOOBS? 
Hoobs


* Which version of Homebridge/HOOBS do you have?
3.3.5


* Which version of this plugin (homebridge-ewelink) do you have? Has the issue started since upgrading from a previous version?
6.1.2


* Which eWeLink devices do you have that are causing issues? Please include product models if applicable.
Sonof L1


* Do you use your main eWeLink credentials or do you use a secondary eWeLink account for Homebridge?
Secondary


### Please paste any relevant logs below.
<!-- ABOUT LOGS
   → More thorough logging can be seen by enabling 'Debug Logging' and
     ...'Request & Response Logging' in the plugin settings.
   → If you are posting an error then it is helpful for me to also see
     ...the previous few lines as this can show the cause of the error.
   → Please enter the logs between the two ``` lines below so that
     ...the logs are formatted in a way which is easier to read.
-->
The write handler for the characteristic 'On' on the accessory 'Light Led' was slow to respond!
The write handler for the characteristic 'On' on the accessory 'Light Led' didn't respond at all!. Please check that you properly call the callback!

```

```
