Fix params sending for job execution

[leonardola]

Hello, I've tried using this sdk for starting jobs with parameters but had to modify it to make it work properly. Every time i tried sending parameters they would not appear on jenkins. So I debugged a little and found out that the way the parameters were sent by the library was wrong.

• First there is no need to use the /buildWithParameters url
• Second it is needed to send all parameters inside an array like this on curl_postFields

array(
    'json' => json_encode(array(
        "parameter" => $parameters
    )
)

I don't know if an update from jenkins itself broke the integration or if the integration never worked properly. This is just the way I fixed it for me. There is probably a better way for mantaining compatibility. If someone propose it, I will be glad to implement.