[TxMt] Can TextMate::UI.alert etc. be used with the ruby20 shim?

[Stefan Daschek]

Following up on 
https://github.com/noniq/Markdown-MathJax.tmbundle/commit/6d003d9c9808acc95414a1b0618640de2380b646#commitcomment-18635004 
I created a very simple test script:

     #!/usr/bin/env ruby20
     require "#{ENV['TM_SUPPORT_PATH']}/lib/ui"
     TextMate::UI.alert(:warning, 'Title', 'Message', 'OK')

Running this gives an “ArgumentError: An object in the argument tree 
could not be converted” in method to_plist in ui.rb at line 54.

If I change the script to use the `ruby18` shim, it works as intended.
Is this expected behaviour or am I doing something wrong?


Stefan