Warning when installing with yarn
When i use `html-sketchapp` with yarn I get the following warning:

```sh
yarn install v1.12.3
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
warning @brainly/html-sketchapp@4.0.1: The engine "sketch" appears to be invalid.
[3/4] 🔗  Linking dependencies...
```

Is there a way to make this valid? Is this the correct place for the sketch version? I don't think this can get checked in any meaningful way.