Fixed singular -> plural in variable

SamiTwigExtension.php

@@ -777,7 +777,7 @@ class SamiTwigExtension extends \Twig_Extension {
 
         if (!empty($interfaces)) {
             foreach($interfaces as $key => $interface)
-                $interface[$key] = self::render_class($interface);
+                $interfaces[$key] = self::render_class($interface);
             array_unshift($i, "## Interfaces");
         }