Ehsan Majdabadi

Results 2 issues of Ehsan Majdabadi

According to the [contentful-migration documentation](https://github.com/contentful/contentful-migration#changefieldcontrol-fieldid-widgetnamespace-widgetid-settings--void), the second parameter of the `changeFieldControl` should be `"extension"` for the custom UI extensions. I created a PR to fix the issue. https://github.com/deluan/contentful-migrate/pull/191