* lib/fileutils.rb (FileUtils#chown, FileUtils#chown_R): Fix the
  wrong output message when user is nil, which should be "chown
  :group file" instead of "chown group file".

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41796 b2dd03c8-39d4-4d8f-98ff-823fe69b080e