Use new Twig_SimpleFunction class

Twig_Function_Method has been removed from Sf framework. 
So we have to use Twig_SimpleFunction.

Twig/MasevExtension.php

@@ -12,7 +12,7 @@ public function __construct($configResolver) {
 
     public function getFunctions() {
         return array(
-            'getMasevSettings' => new \Twig_Function_Method($this, 'getMasevSettings')
+            new \Twig_SimpleFunction('getMasevSettings', [$this, 'getMasevSettings'])
         );
     }
 
@@ -29,4 +29,4 @@ public function getName()
     {
         return 'masev_extension';
     }
-}
+}