Use to_reference menthod when render issue id in list

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/projects/issues/_issue.html.haml

@@ -29,7 +29,7 @@
             = 0
     .issue-info
-      = "##{issue.iid} opened #{time_ago_with_tooltip(issue.created_at, placement: 'bottom')} by #{link_to_member(@project, issue.author, avatar: false)}".html_safe
+      = "#{issue.to_reference} opened #{time_ago_with_tooltip(issue.created_at, placement: 'bottom')} by #{link_to_member(@project, issue.author, avatar: false)}".html_safe
       - if issue.votes_count > 0
         = render 'votes/votes_inline', votable: issue
       - if issue.milestone