update version to 2.8.0

Author: maximilientyc

src/Stuart/Infrastructure/HttpClient.php

@@ -85,7 +85,7 @@ private function defaultHeaders()
     {
         return [
             'Authorization' => 'Bearer ' . $this->authenticator->getAccessToken(),
-            'User-Agent' => 'stuart-php-client/2.6.0',
+            'User-Agent' => 'stuart-php-client/2.8.0',
             'Content-Type' => 'application/json'
         ];
     }

tests/Stuart/tests/Infrastructure/HttpClientTest.php

@@ -17,7 +17,7 @@ class HttpClientTest extends \PHPUnit_Framework_TestCase
 
     private $container;
 
-    const PHP_CLIENT_USER_AGENT = 'stuart-php-client/2.6.0';
+    const PHP_CLIENT_USER_AGENT = 'stuart-php-client/2.8.0';
 
     public function setUp()
     {