Removed unnecessary `to_a` call

`Dir.entries` returns an array.

test/ruby/test_dir.rb

@@ -318,7 +318,7 @@ class TestDir < Test::Unit::TestCase
 
   def test_entries
     assert_entries(Dir.open(@root) {|dir| dir.entries})
-    assert_entries(Dir.entries(@root).to_a)
+    assert_entries(Dir.entries(@root))
     assert_raise(ArgumentError) {Dir.entries(@root+"\0")}
   end