use 2.8 as the default server version

lib/Predis/Profile/ServerProfile.php

@@ -78,7 +78,7 @@ abstract class ServerProfile implements ServerProfileInterface, CommandProcessin
             '2.4'     => 'Predis\Profile\ServerVersion24',
             '2.6'     => 'Predis\Profile\ServerVersion26',
             '2.8'     => 'Predis\Profile\ServerVersion28',
-            'default' => 'Predis\Profile\ServerVersion26',
+            'default' => 'Predis\Profile\ServerVersion28',
             'dev'     => 'Predis\Profile\ServerVersionNext',
         );
     }

tests/Predis/Profile/ServerProfileTest.php

@@ -19,7 +19,7 @@ use Predis\Command\Processor\ProcessorChain;
  */
 class ServerProfileTest extends PredisTestCase
 {
-    const DEFAULT_PROFILE_VERSION = '2.6';
+    const DEFAULT_PROFILE_VERSION = '2.8';
     const DEVELOPMENT_PROFILE_VERSION = '3.0';
 
     /**