prefer arrow functions

Signed-off-by: marcin mikołajczak <git@mkljczk.pl>

src/ready.ts

@@ -1,7 +1,9 @@
-export default function ready(loaded: () => void): void {
+const ready = (loaded: () => void): void => {
   if (['interactive', 'complete'].includes(document.readyState)) {
     loaded();
   } else {
     document.addEventListener('DOMContentLoaded', loaded);
   }
-}
+};
+
+export default ready;