breadcrumbs with gretel gem working on dev environment but not working on production environment on Heroku

i am working in a website hosted on Heroku, i used gretel gem for making breadcrumbs.
the breadcrumbs is working fine on dev environment but in Heroku this does not work.
On Heroku the breadcrumbs look like this:

I not have idea why this not working on Heroku. if this working very fine on dev environment
any idea?
Breadcrumbs code: 
crumb :root do
  link "Galeria", root_path
end

crumb :category do |category|
  link "Categoria: #{category.name.titleize}", category
  parent :root
end

crumb :picture do |picture, category|
  link "Viendo la imagen: #{picture.title.titleize}"
  parent :category, category
end

Layout with breadcrumb:
.container
  = breadcrumbs pretext: "Estas en: ", display_single_fragment: true, style: :bootstrap

Sorry my bad english...

well. i answer myself.
reading the  slim documentation.
i found that I must use == symbol instead = to avoid escaped html code.