chore(internal): refactor array check

Author: stainless-app[bot]

packages/mcp-server/src/headers.ts

@@ -6,7 +6,7 @@ import { IncomingMessage } from 'node:http';
 
 export const parseAuthHeaders = (req: IncomingMessage): Partial<ClientOptions> => {
  const apiKey =
- req.headers['x-nextbillion-sdk-api-key'] instanceof Array ?
+ Array.isArray(req.headers['x-nextbillion-sdk-api-key']) ?
  req.headers['x-nextbillion-sdk-api-key'][0]
  : req.headers['x-nextbillion-sdk-api-key'];
  return { apiKey };