Incorrect variable name used in curl.php

Incorrect variable name used for the user agent string.

libraries/joomla/http/transport/curl.php

@@ -120,7 +120,7 @@ public function request($method, JUri $uri, $data = null, array $headers = null,
 		// If an explicit user agent is given use it.
 		if (isset($userAgent))
 		{
-			$headers[CURLOPT_USERAGENT] = $userAgent;
+			$options[CURLOPT_USERAGENT] = $userAgent;
 		}
 
 		// Set the request URL.