Use RUBY insted of BUNDLE_RUBY for test-bundled-gems of ruby/ruby.

Author: hsbt

test/helper.rb

@@ -28,7 +28,7 @@ class TaskManager
     include Rake::TaskManager
   end
 
-  RUBY = File.realpath(ENV["BUNDLE_RUBY"] || Gem.ruby)
+  RUBY = File.realpath(ENV["RUBY"] || Gem.ruby)
 
   def setup
     ARGV.clear