feat(types): add expiresAt field to Invite interface (#880)

Reference: https://github.com/discord/discord-api-docs/commit/6dc1b2a3e7aad5145420f965e3ec15f3b7ed7074

src/types/invites/invite.ts

@@ -24,4 +24,6 @@ export interface Invite {
   approximatePresenceCount?: number;
   /** Approximate count of total members */
   approximateMemberCount?: number;
+  /** The expiration date of this invite, returned from the `GET /invites/<code>` endpoint when `with_expiration` is `true`. */
+  expiresAt?: string | null;
 }