use time() instead of current_datetime() for WP 4.x compatibility (#6)

The function current_datetime() has been introduced in WP 5.3, but
the Plugin should maintain compatibility with 4.x for now.

includes/class-scliveticker.php

@@ -206,7 +206,7 @@ public static function shortcode_ticker_show( $atts ) {
  $output .= ' sclt-ajax" '
  . 'data-sclt-ticker="' . $ticker . '" '
  . 'data-sclt-limit="' . $limit . '" '
- . 'data-sclt-last="' . current_datetime()->getTimestamp();
+ . 'data-sclt-last="' . time();
  }
  $output .= '"><ul>';
 
@@ -362,13 +362,13 @@ public static function ajax_update() {
  $res[] = array(
  'w' => $slug,
  'h' => $out,
- 't' => current_datetime()->getTimestamp(),
+ 't' => time(),
  );
  } else {
  $res[] = array(
  's' => $slug,
  'h' => $out,
- 't' => current_datetime()->getTimestamp(),
+ 't' => time(),
  );
  }
  }