log output from activemodel's railtie_test directly to STDOUT

after this patch, running the tests in activemodel will no longer
create an untracked log/ folder inside of activemodel

activemodel/test/cases/railtie_test.rb

@@ -9,6 +9,7 @@ def setup
 
     @app ||= Class.new(::Rails::Application).tap do |app|
       app.config.eager_load = false
+      app.config.logger = Logger.new(STDOUT)
     end
   end