Escalate missing error when :raise is true

Before ec16ba75a5493b9da972eea08bae630eba35b62f,  `ActionView::Helpers::TranslationHelper#translate` has raised errors with specifying `options[:raise]` to `true`.

This should work by this fix:

``` ruby
begin
  t(:"translations.missing", raise: true)
rescue I18n::MissingTranslationData
  p :hello!
end
```