fix: Handle different `execute` return values for wdio v4 support (#99)
fix: Handle different `execute` return values for wdio v4 support (#99)

Turns out WebdriverIO v4's `execute` command returns an object with the value of what's returned from that function, `sessionId`, and the `status`:

```js
{ sessionId: "2323weinof", value: 'returnValueOfFunction',  _status: 0 }
```

WebdriverIO v5 just returns what is returned from the function. This PR allows us to handle both cases. 

I wish this was easy to test. I confirmed manually this works with our example app using this branch (downgraded to v4): https://github.com/percy/example-webdriverio/tree/rd/wdio4
percy/percy-webdriverio,percy/percy-webdriverio