Bracket attributes no longer support empty lines

[paulcretu]

I upgraded from 0.4.0 to 0.5.0 and multiline attributes that contain empty lines no longer work. For example:

ember-component [
  isHidden=foo
  value=bar

  saveAction="save" ]

Lines that contain comments don't work either:

ember-component [
  isHidden=foo
  value=bar
  / here's a comment
  saveAction="save" ]

[bantic]

@paulcretu Thanks for this report. This likely relates to #219 as well.