Option dest does not support function for cjs output

[ilyavf]

As described in steal-tools/ExportOutput
dest can be a function. But in the following example its getting ignored (if its a string then its OK):

stealTools.export({
  steal: {
    config: 'package.json!npm',
    main: 'myprop/index'
  },
  outputs: {
    '+cjs': {
      dest: function(moduleName){
            // --- ---- is not getting called.
            return __dirname+"/"+moduleName+".js";
      }
    }
  }
});

[matthewp]

The code for this stuff is in this folder: https://github.com/stealjs/steal-tools/tree/master/lib/build/helpers