Fix engines test

Signed-off-by: José Valim <jose.valim@gmail.com>

railties/test/railties/engine_test.rb

@@ -62,12 +62,14 @@ def initialize(app)
 
       def call(env)
         response = @app.call(env)
-        response[2].upcase!
+        response[2].each { |b| b.upcase! }
         response
       end
     end
 
     test "engine is a rack app and can have his own middleware stack" do
+      add_to_config("config.action_dispatch.show_exceptions = false")
+
       @plugin.write "lib/bukkits.rb", <<-RUBY
         class Bukkits
           class Engine < ::Rails::Engine