Modifications to work with Bootstrap 4.6

In order to make this look correct in my app, I had to do the following changes:

@line 114 I added:

```javascript
this.$element.addClass('form-control');
this.$element.removeClass('ml-3');
```

When I put these lines in, it looks very nice and the dropdown lines up with the input.  I post this to see if anyone had any better way of doing this.
