Multicolor missing alpha control

[pvigilante]

Issue description:

Since the update to WordPress 4.9 and the latest Kirki, it appears that the alpha selector for the multicolor field is disabled. Adding the option to the array as 'alpha' => true does not work as it did with previous versions. I know the latest version requires the option to be set in the 'choices' array for the standard 'color' field type, but this just creates a new color selector.

When I hard code in the value for data-alpha to be true, it brings back the alpha selector. However, the styling is off.

As of version 3.0.15 and WP 4.9

When hardcoded to activate alpha property:

Used to be, from version 2.3.4, pre WP 4.9

Version used:

3.0.16

Using theme_mods or options?

theme_mods

Code to reproduce the issue (config + field(s))

Kirki::add_field( 'hiiwp', array(
'type' => 'multicolor',
'settings' => 'typography_button_default_border_color',
'label' => ( 'Border Color (.button)', 'hiiwp' ),
'section' => $section,
'choices' => array(
'base' => esc_attr( 'Base Color', 'hiiwp' ),
'hover' => esc_attr__( 'Hover Color', 'hiiwp' ),
),
'alpha' => true,
'default' => $hiilite_options['typography_button_default_border_color'],
'priority' => 1,
) );