Goutte\Client::setHeader PHP Method

    public function setHeader($name, $value)
    {
        $this->headers[strtolower($name)] = $value;
        return $this;
    }

 private function setUpClient()
 {
     $this->client = new Client();
     $this->client->setHeader('User-Agent', $this->user_agent);
     $this->client->setHeader('Accept-Language', 'en-gb');
     $this->client->setClient(new \GuzzleHttp\Client(['allow_redirects' => false, 'cookies' => true, 'verify' => false, 'proxy' => ['http' => $this->proxy]]));
 }