Update event helper to display target_iid in event title instead of target_id.

The event helper is used extensively within the dashboard atom feed, so by
fixing this, we fixed #303.

app/helpers/events_helper.rb

@@ -45,15 +45,15 @@ module EventsHelper
 
   def event_feed_title(event)
     if event.issue?
-      "#{event.author_name} #{event.action_name} issue ##{event.target_id}: #{event.issue_title} at #{event.project_name}"
+      "#{event.author_name} #{event.action_name} issue ##{event.target_iid}: #{event.issue_title} at #{event.project_name}"
     elsif event.merge_request?
-      "#{event.author_name} #{event.action_name} MR ##{event.target_id}: #{event.merge_request_title} at #{event.project_name}"
+      "#{event.author_name} #{event.action_name} MR ##{event.target_iid}: #{event.merge_request_title} at #{event.project_name}"
     elsif event.push?
       "#{event.author_name} #{event.push_action_name} #{event.ref_type} #{event.ref_name} at #{event.project_name}"
     elsif event.membership_changed?
       "#{event.author_name} #{event.action_name} #{event.project_name}"
     elsif event.note?
-      "#{event.author_name} commented on #{event.note_target_type} ##{truncate event.note_target_id} at #{event.project_name}"
+      "#{event.author_name} commented on #{event.note_target_type} ##{truncate event.note_target_iid} at #{event.project_name}"
     else
       ""
     end