Validation bug?

Hey! 
We've created the following property:
```
{
    "type": "number",
    "description": "some description",
    "x-env-value": "ENV_PROP",
    "default": false
}
```

It passed the package's validation using `npm run validation`. `default: false` of course is wrong.
For default `false`, I think the validation should fail. 
What do you think?