Plugin doesn't see Ruby neither Slim

[Askhat Bikmetov]

I've added gem 'slim' to Gemfile, and installed it with bundle install --path=vendor/bundle. Then I've defined this task in Gruntfile.coffee:

slim:
  dst:
    options:
      bundleExec: true
      pretty: true
    files: 'dst/index.html' : 'src/index.slim'

Now grunt slim returns exactly that:

Running "slim:dst" (slim) task
Warning: You need to have Ruby and Slim installed and in your PATH for
this task to work. More info:
https://github.com/matsumos/grunt-slim Use --force to continue.

But ruby -v returns ruby 2.0.0p481 (2014-05-08 revision 45883) [universal.x86_64-darwin14], and bundle exec slimrb -v returns Slim 3.0.6.
Am I mistaken by myself or it's a bug?

BTW grunt-contrib-haml which is looks pretty same for me works well.