Use Organisation#name_with_abbreviation method

This wasn't being used in the organisations index. We had custom logic
which resulted in organisations without abbreviations having empty
brackets after their name, which looked odd. This method separates the
name and abbreviation with a dash rather than putting the abbreviation
in brackets, but there doesn't seem to be an obvious reason why both
uses can't be the same

The dash used in the method was a non-standard character, so that's
fixed here

app/models/organisation.rb

@@ -19,7 +19,7 @@ class Organisation < ApplicationRecord
 
   def name_with_abbreviation
     return_value = if abbreviation.present? && abbreviation != name
-                     "#{name} – #{abbreviation}"
+                     "#{name} - #{abbreviation}"
                    else
                      name
                    end

app/views/organisations/index.html.erb

@@ -11,7 +11,7 @@
   <%= t.body do %>
     <% @organisations.each do |organisation| %>
       <%= t.row do %>
-        <%= t.cell "#{organisation.name} (#{organisation.abbreviation})" %>
+        <%= t.cell "#{organisation.name_with_abbreviation}" %>
         <%= t.cell organisation.organisation_type %>
         <%= t.cell organisation.slug %>
         <td class="govuk-table__cell">