minor

Author: Nyholm

lib/Github/Client.php

@@ -123,7 +123,7 @@ public function __construct(Builder $httpClientBuilder = null, $apiVersion = nul
         )));
 
         $this->apiVersion = $apiVersion ?: 'v3';
-        $this->getHttpClientBuilder()->addHeaders(['Accept' => sprintf('application/vnd.github.%s+json', $this->apiVersion)]);
+        $builder->addHeaders(['Accept' => sprintf('application/vnd.github.%s+json', $this->apiVersion)]);
 
         if ($enterpriseUrl) {
             $this->setEnterpriseUrl($enterpriseUrl);