Update types

Make sure types are declared correctly.

src/index.ts

@@ -136,8 +136,8 @@ const DEFAULT_CARDS: string[] = [
   "You don't have to be ashamed of using your own ideas", //
 ];
 
-export const getDefaultCards = () => DEFAULT_CARDS;
+export const getDefaultCards = (): string[] => DEFAULT_CARDS;
 
-export const generate = (cards = getDefaultCards()) => (
+export const generate = (cards = getDefaultCards()): string => (
   cards[Math.floor(Math.random() * cards.length)]
 );