Format milestone header as issues and MRs

* Enclose the identifier in strong
* Use the % character as in GFM
* Remove spaces around en dash for date range

app/helpers/milestones_helper.rb

@@ -97,7 +97,7 @@ module MilestonesHelper
 
   def milestone_date_range(milestone)
     if milestone.start_date && milestone.due_date
-      "#{milestone.start_date.to_s(:medium)} - #{milestone.due_date.to_s(:medium)}"
+      "#{milestone.start_date.to_s(:medium)}–#{milestone.due_date.to_s(:medium)}"
     elsif milestone.due_date
       if milestone.due_date.past?
         "expired on #{milestone.due_date.to_s(:medium)}"

app/views/projects/milestones/show.html.haml

@@ -16,10 +16,9 @@
         Open
     .header-text-content
       %span.identifier
-        Milestone ##{@milestone.iid}
+        %strong
+          Milestone %#{@milestone.iid}
       - if @milestone.due_date || @milestone.start_date
-        %span.creator
-          ·
         = milestone_date_range(@milestone)
     .milestone-buttons
       - if can?(current_user, :admin_milestone, @project)