deepmerge in defaultSchmea merge function

In defaultSchema merge function you have:

```js
const merged = merge({}, this, ...schemas)
```
is there a reason for using lodash' deepMerge instead of a simple reduce:

```js
const merged = schemas.reduce((merged, schema) => ({...merged, ...schema}), this)
```

Using lodash merge makes it incredibly slow with a lot of refs to other schemas and even worse if you want to use self referencing