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/**
 * enqueue scripts and styles 
 *
 */

function nr_load_scripts() {
        
    wp_register_script('googlemaps', 'https://maps.googleapis.com/maps/api/js?key=AIzaSyCxucarwzsej2hTS4d89VnYICal7OB6-cw',null,null,true);  
    wp_enqueue_script('googlemaps');
        
}
add_action( 'wp_enqueue_scripts', 'nr_load_scripts' );


http://matthewhorne.me/defer-async-wordpress-scripts/