typeCast config option is getting deleted/ignored

```js
const mconfig = {
config: {
dev: {
driver: 'mysql',
host: '', db: '', ....,
typeCast: (field, next) => {} // this is getting removed or ignored
},
'sql-file': true
},
env: 'dev'
}

Migrate.getInstance(true, mConfig, callback);
```

I tried to find where or why but couldn't find it

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