Spacing of table column headings does not apply correctly to a table that is not in a panel.

[Alonsormm]

Describe the bug
The spacing of table column headings does not apply correctly to a table that is not in a panel.

To Reproduce
Steps to reproduce the behavior:

1. Adds a table_for component in a show of a resource. (The code is taken from the demo)

show do
  attributes_table do
    row :name
    row :state
  end

  orders = Order.where(book: book)
  show do
  attributes_table do
    row :name
    row :state
  end

  orders = Order.where(book: book)
  table_for orders, sortable: false do
    column :reference
    column :state
    column :created_at     
    column do |order|
      span link_to 'View', order_path(order), class: 'small button action'
      span link_to 'Edit', edit_order_path(order), class: 'small button action'
    end     
  end
end

Expected behavior
The spacing of table column headings should be the same regardless of whether it is within a panel.

Screenshots
With panel:

Without panel:

Gemfile

arctic_admin (3.2.0)
      activeadmin (>= 1.1.0, < 3.0)
      font-awesome-sass (~> 5.0)
      jquery-rails