Introduce X-XSS-Protection header

Change-Id: I1b85d04743361343a09ca6d32593720a991a9e9f
diff --git a/lib/Kalamar.pm b/lib/Kalamar.pm
index a7c360b..1dbc373 100644
--- a/lib/Kalamar.pm
+++ b/lib/Kalamar.pm
@@ -113,6 +113,7 @@
       my $h = shift->res->headers;
       $h->header('X-Content-Type-Options' => 'nosniff');
       $h->header('X-Frame-Options' => 'sameorigin');
+      $h->header('X-XSS-Protection' => '1; mode=block');
       $h->header(
         'Access-Control-Allow-Methods' =>
           $h->header('Access-Control-Allow-Methods') // 'GET, POST, OPTIONS'