Improve type safety

src/routes/+page.svelte

@@ -25,7 +25,7 @@
   }
 
   const refreshInterval = parseInt(PUBLIC_REFRESH_INTERVAL);
-  let interval: NodeJS.Timer | null = null;
+  let interval: ReturnType<typeof setTimeout> | null = null;
   let moreOlderPostsAvailable = true;
   let loadingOlderPosts = false;