Fix failing test that used a method hash_for removed for rack-test

Author: Tejas Mandke

test/action_controller_test.rb

@@ -127,7 +127,7 @@ def test_getting_session_value_after_session_reset
       get '/set_session_value'
       assert_response :success
       assert cookies['_session_id']
-      session_cookie = cookies.send(:hash_for)['_session_id']
+      session_cookie = cookies.get_cookie '_session_id'
 
       get '/call_reset_session'
       assert_response :success