Log Message:
Update ruby-haml to 4.0.7.

Add pkg_alternative support.

# Haml Changelog

## 4.0.7

Released on August 10, 2015
([diff](https://github.com/haml/haml/compare/4.0.6...4.0.7)).

* Significantly improve performance of regexp used to fix whitespace handling in \ 
textareas (thanks [Stan Hu](https://github.com/stanhu)).