[TxMt] change default ruby

[Sune Foldager]

Ruby scripts launched from TM are fed directly to the ruby  
interpreter so unless IT interprets the shebang (and I don't think  
so), putting one at the start will be ignored.

As for using env... well, in the Run Ruby command, ruby is started  
like this:  ruby
..and given that shell commands started from TM enjoy a full login- 
shell setup, your PATH should also be correct, leading to the 'usual'  
ruby being invoked.

-- Sune.