Multiline attribute syntax is not highlighted

[amacdougall]

A component in this form is highlighted correctly:

= component-name attr-one=value attr-two="text value"

But a component in this form is not:

= component-name [
  attr-one=value
  attr-two="text value"
]

I have made a small fix in my local copy of the syntax file. I'd be happy to submit a pull request.