Don't upgrade config.file_watcher during upgrade path

railties/lib/rails/generators/rails/app/app_generator.rb

@@ -95,9 +95,14 @@ def config_when_updating
       action_cable_config_exist = File.exist?('config/cable.yml')
       ssl_options_exist = File.exist?('config/initializers/ssl_options.rb')
       rack_cors_config_exist = File.exist?('config/initializers/cors.rb')
+      development_config_exist = File.exist?('config/environments/development.rb')
 
       config
 
+      if development_config_exist
+        gsub_file 'config/environments/development.rb', /^(\s+)config\.file_watcher/, '\1# config.file_watcher'
+      end
+
       unless callback_terminator_config_exist
         remove_file 'config/initializers/callback_terminator.rb'
       end