Tell I18n not to validate locales in spec

Validation will be the default in a future Rails release.
Remove Haml::MagicTranslations::Tasks as update_pofiles is no more

gettext 3.1 removed the `update_pofiles` method. Their new Rake task definition
API is simple enough so we can simply tell users to add the custom parser
manually in their Rakefile.
Bump minor version number

The removal of Haml::MagicTranslations::Tasks is an API breakage. Let's be
clear about it.
Update gemspec