fix: incomplete predicate (#56)

Seems like an unintentional typo. I'm just came across this code while looking for cookie handling in Next, I haven't run into an issue and haven't used the package in my project. This was just something I noticed.

src/index.ts

@@ -17,7 +17,7 @@ const isCookiesFromAppRouter = (
 ): cookieStore is AppRouterCookies => {
   if (!cookieStore) return false;
   return (
-    'getAll' &&
+    'getAll' in cookieStore &&
     'set' in cookieStore &&
     typeof cookieStore.getAll === 'function' &&
     typeof cookieStore.set === 'function'