test_dir_m17n.rb: sort Dir.entries

* test/ruby/test_dir_m17n.rb (test_entries_compose): the order on the
  filesystem does not matter, so sort Dir.entries result to compare.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40875 b2dd03c8-39d4-4d8f-98ff-823fe69b080e