Update ruby-haml to 4.0.3.

## 4.0.3

Released May 21, 2013 ([diff](https://github.com/haml/haml/compare/4.0.2...4.0.3)).

* Compatibility with newer versions of Rails's Erubis handler.
* Fix Erubis handler for compatibility with Tilt 1.4.x, too.
* Small performance optimization for html_escape.
(thanks [Lachlan Sylvester](https://github.com/lsylvester))
* Documentation fixes.
* Documented some helper methods that were left out of the reference.
(thanks [Shane Riley](https://github.com/shaneriley))

## 4.0.2

Released April 5, 2013 ([diff](https://github.com/haml/haml/compare/4.0.1...4.0.2)).

* Explicitly require Erubis to work around bug in older versions of Tilt.
* Fix :erb filter printing duplicate content in Rails views.
(thanks [Jori Hardman](https://github.com/jorihardman))
* Replace range with slice to reduce objects created by `capture_haml`.
(thanks [Tieg Zaharia](https://github.com/tiegz))
* Correct/improve some documentation.

## 4.0.1

Released March 21, 2013 ([diff](https://github.com/haml/haml/compare/4.0.0...4.0.1)).

* Remove Rails 3.2.3+ textarea hack in favor of a more general solution.
* Fix some performance regressions.
* Fix support for Rails 4 `text_area` helper method.
* Fix data attribute flattening with singleton objects.
(thanks [Alisdair McDiarmid](https://github.com/alisdair))
* Fix support for sass-rails 4.0 beta.
(thanks [Ryunosuke SATO](https://github.com/tricknotes))
* Load "haml/template" in Railtie in order to prevent user options set in a
  Rails initializer from being overwritten
* Don't depend on Rails in haml/template to allow using Haml with ActionView
  but without Rails itself. (thanks [Hunter Haydel](https://github.com/wedgex))

(taca)