Update index.d.ts

Updating Cookie options to follow Express documentation https://expressjs.com/en/api.html#res.cookie

Two properties `encode` and `sameSite` were missing

express-serve-static-core/index.d.ts

@@ -161,6 +161,8 @@ interface CookieOptions {
     path?: string;
     domain?: string;
     secure?: boolean | 'auto';
+    encode?: (val: string) => void;
+    sameSite?: boolean | string;
 }
 
 interface Errback { (err: Error): void; }