Fix build error

Author: fabon-f

src/datetime/_utcTimeStamp.ts

@@ -6,7 +6,7 @@ export function utcTimeStamp(
 	minute = 0,
 	second = 0,
 	millisecond = 0,
-) {
+): number {
 	const date = new Date();
 	date.setUTCFullYear(year, month - 1, day);
 	date.setUTCHours(hour, minute, second, millisecond);