Gabriel González Zabala said almost 4 years ago on Using Bootstrap Themes :
  Thanks for you answer. I thought the same but I followed the tutorial and make sure that there is no references in the application layout file.
Weird thing is that is working for the stylesheets but not the js...
This is my application layout:

<!DOCTYPE html>
<html>
  <head>
    <title>Blog</title>
    <%= csrf_meta_tags %>
    <%= csp_meta_tag %>

    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <%= stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track': 'reload' %>

    <%= javascript_pack_tag 'application', 'data-turbolinks-track': 'reload', defer: true %>
    <%= stylesheet_pack_tag 'application', 'data-turbolinks-track': 'reload', defer: true %>

    <!-- Custom fonts for this template -->
    <link href="https://fonts.googleapis.com/css?family=Saira+Extra+Condensed:500,700" rel="stylesheet">
    <link href="https://fonts.googleapis.com/css?family=Muli:400,400i,800,800i" rel="stylesheet">

  </head>

  <body id="page-top">
    <%= render 'layouts/navigations/sidebar' %>

    <div class="container-fluid p-0">

      <section class="resume-section p-3 p-lg-5 d-flex align-items-center" id="about" style="background-color: #100C08;">
        <%= yield %>
      </section>

      <hr class="m-0">

      <%= render 'layouts/navigations/experience' %>

      <hr class="m-0">

      <%= render 'layouts/navigations/education' %>

      <hr class="m-0">

      <%= render 'layouts/navigations/skills' %>

      <hr class="m-0">

      <%= render 'layouts/navigations/interests' %>

      <hr class="m-0">

     <%= render 'layouts/navigations/awards' %>

    </div>
  </body>
</html>