Readonly textarea shows iOS keyboard accessory view

Readonly textarea opens the iOS keyboard accessory view when using the WKWebView engine.

How to recreate:
1. Install WKWebView engine plugin:
```
cordova platform add ios@4.0.1
cordova plugin add cordova-plugin-wkwebview-engine@1.0.1 --save
```
2. Tap inside a textarea with 'readonly' attribute.
```
<textarea placeholder="readonly" readonly></textarea>
```

What happens:
The iOS keyboard accessory view opens.

What should happen:
Nothing (the same as UIWebView).