RequestException while sending Plivo sms in latest laravel 5.1.26 - sms

Question

I am doing project in laravel. I followed all the steps mentioned in
plivo.com .
As I had done same steps in my another old project and this worked perfectly, but after updating my composer its not working and throwing same error message as like my new laravel project. Error message is as follow,
Fatal error: Uncaught exception 'GuzzleHttp\Exception\RequestException' with message 'cURL error 60: SSL certificate problem: self signed certificate in certificate chain
My Plivo folder is inside the root folder. Guzzle installed is "guzzlehttp/guzzle": "v6.1.1".
composer.json is,
{
"require": {
"plivo/plivo-php": "~1.1.0"
}
}
Controller.php
<?php
namespace App\Http\Controllers;
use Plivo;
public function signup(Request $request){
$number = $request->input('owner_phone');
$output = $this->validatenumber($number);
}
public function validatenumber($number){
$auth_id = "MAZJFKNTU3OGQ5NMM5YJ";
$auth_token = "NDcyYjU5NmMxMmQzMzYzMjIzODExMTg3NzZmOWVj";
$p = new Plivo\RestAPI($auth_id, $auth_token);
$params = array(
'src' => '14154847489', // Sender's phone number with country code
'dst' => '91'.$number, // Receiver's phone number with country code
'text' => 'Your TaaraGo verification code is '.$otpnumber. '.', // Your SMS text message
'url' => 'http://localhost/untitled/sentsms.php', // The URL to which with the status of the message is sent
'method' => 'POST' // The method used to call the url
);
return $response = $p->send_message($params);
}
?>
and route.php is,
Route::post('auth/signup', 'AuthController#signup');
Is there any solution to this problem? any one having same problem with laravel version 5.1.26, give me solution.