fix warning during test execution

[#5997 state:resolved]
Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

actionpack/test/controller/action_pack_assertions_test.rb

@@ -173,7 +173,7 @@ def test_redirect_to_named_route
 
   def test_string_constraint
     with_routing do |set|
-      set.draw do |map|
+      set.draw do
         match "photos", :to => 'action_pack_assertions#nothing', :constraints => {:subdomain => "admin"}
       end
     end