Set app logger

For issue #183 I have the same problem with Rails 4.1.6 and Ruby 2.1 with that, we have covered some cases ^^

lib/google/api_client/railtie.rb

@@ -10,7 +10,13 @@ module Google
     #
     class Railtie < Rails::Railtie
       initializer 'google-api-client' do |app|
-        Google::APIClient.logger = app.logger
+        _logger = case
+                    when app.respond_to?(:logger)        then app.logger
+                    when app.config.respond_to?(:logger) then app.config.logger
+                    else                                      Rails.logger
+                  end
+                  
+        Google::APIClient.logger = _logger
       end
     end
   end