Adding a "Google Plus" profile field to Co-Authors Plus

gistfile1.php

<?php

/**
 * Add a "Google Plus" field to Co-Authors Plus Guest Author
 */
add_filter( 'coauthors_guest_author_fields', 'capx_filter_guest_author_fields', 10, 2 );
function capx_filter_guest_author_fields( $fields_to_return, $groups ) {

	if ( in_array( 'all', $groups ) || in_array( 'contact-info', $groups ) ) {
		$fields_to_return[] = array(
					'key'      => 'google_plus',
					'label'    => 'Google Plus',
					'group'    => 'contact-info',
				);
	} 

	return $fields_to_return;
}