Element not reachable by keyboard

#### What are you trying to achieve?

Fill a field in a shadow dom

#### What do you get instead?

I get the following error

> Provide console output if related. Use `--verbose` mode for more details.

```bash
I.seeElement({ shadow: ['.employer', 'input']})
Emitted | step.before (I see element {"shadow":[".employer","input"]})
Emitted | step.after (I see element {"shadow":[".employer","input"]})
Emitted | step.start (I see element {"shadow":[".employer","input"]})
I see element {"shadow":[".employer","input"]}
› [Elements] Found 1 'shadow' elements
Emitted | step.passed (I see element {"shadow":[".employer","input"]})
Emitted | step.finish (I see element {"shadow":[".employer","input"]})
OK I.seeElement({ shadow: ['.employer', 'input']})
I.fillField({ shadow: ['.employer', 'input']}, 'hi')
Emitted | step.before (I fill field {"shadow":[".employer","input"]}, "hi…
Emitted | step.after (I fill field {"shadow":[".employer","input"]}, "hi")
Emitted | step.start (I fill field {"shadow":[".employer","input"]}, "hi")
I fill field {"shadow":[".employer","input"]}, "hi"
› [Elements] Found 1 'shadow' elements
[1] Retrying... Attempt #2
› [Elements] Found 1 'shadow' elements
[1] Retrying... Attempt #3
› [Elements] Found 1 'shadow' elements
[1] Retrying... Attempt #4
› [Elements] Found 1 'shadow' elements
[1] Error | element not interactable: Element is not reachable by keyboard
```

### Details

* CodeceptJS version: 2.6.2
* NodeJS Version: 12.14.1
* Operating System: Ubuntu 18.04.4 LTS
* webdriverio
* geckodriver: 1.19
* @wdio/selenium-standalone-service: 5.16.10
* Configuration file:

```js
exports.config = {
tests: './steps/*.js',
output: './output',
helpers: {
WebDriver: {
url: 'http://example.com',
browser: 'firefox',
host: '127.0.0.1',
port: 4444,
restart: false,
windowSize: '1920x1680'
}
},
include: {
I: './steps.js'
},
bootstrap: null,
mocha: {},
name: 'functional',
plugins: {
retryFailedStep: {
enabled: true
},
screenshotOnFail: {
enabled: true
},
wdio: {
enabled: true,
services: ['selenium-standalone']
}
}
}
```