webdriver: add missed return types for jsonwp (#3812)
webdriver: add missed return types for jsonwp (#3812)

## Proposed changes
Some return types were missed in jsonwp. But `https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol` when I make search by `Returns:` I see 43 findings. In our jsonwp.json 47 matches. But when I started searching I found that some returns missed on the site, so I decided not check again all our commands with returns. 

[//]: # (Describe the big picture of your changes here to communicate to the maintainers why we should accept this pull request. If it fixes a bug or resolves a feature request, be sure to link to that issue.)

## Types of changes

[//]: # (What types of changes does your code introduce to WebdriverIO?)
[//]: # (_Put an `x` in the boxes that apply_)

- [x] Bugfix (non-breaking change which fixes an issue)

## Checklist

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- [x] I have read the [CONTRIBUTING](https://github.com/webdriverio/webdriverio/blob/master/CONTRIBUTING.md) doc

## Further comments

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### Reviewers: @webdriverio/technical-committee

webdriverio/webdriverio,webdriverio/webdriverio,webdriverio/webdriverio