fix further type problems

src/lib/helper/shortenFileSize.ts

@@ -2,12 +2,7 @@ const KILO = 1024;
 const MEGA = KILO * KILO;
 const GIGA = MEGA * KILO;
 
-/**
- * Shortens the size in bytes
- * @param {number} size
- * @returns{string}
- */
-export default function shortenFileSize(size: number) {
+export default function shortenFileSize(size: number): string {
 	const giga = Math.floor(size / GIGA);
 	let remainder = size % GIGA;
 	const mega = Math.floor(remainder / MEGA);