Fixed HTML escaping after call to html_tag

The old value of _haml_concat_raw was not being set correctly, hence
calls to haml_concat after a call to haml_tag would result in the output
of haml_concat being appeneded unescaped.

Resolves #718
Prepped release
Bump version to beta.1

[ci skip]
Add gem version badge
Loosen minitest dependency.  Add Gemfile for Rails 4.1.0.beta1

Remove the branches restriction from Travis config.

Get Rubinius running again

Add Rubinius gems