bin: get closer from the default template of Rails 6

bin/update

@@ -1,6 +1,5 @@
 #!/usr/bin/env ruby
 require 'fileutils'
-include FileUtils
 
 # path to your application root.
 APP_ROOT = File.expand_path('..', __dir__)
@@ -9,7 +8,7 @@ def system!(*args)
   system(*args) || abort("\n== Command #{args} failed ==")
 end
 
-chdir APP_ROOT do
+FileUtils.chdir APP_ROOT do
   # This script is a way to update your development environment automatically.
   # Add necessary update steps to this file.