Filter current user to the top of issue assignee list

app/views/shared/issuable/_context.html.haml

@@ -9,7 +9,7 @@
         none
     .issuable-context-selectbox
       - if can?(current_user, :"admin_#{issuable.to_ability_name}", @project)
-        = users_select_tag("#{issuable.class.table_name.singularize}[assignee_id]", placeholder: 'Select assignee', class: 'custom-form-control js-select2 js-assignee', selected: issuable.assignee_id, project: @target_project, null_user: true, current_user: true)
+        = users_select_tag("#{issuable.class.table_name.singularize}[assignee_id]", placeholder: 'Select assignee', class: 'custom-form-control js-select2 js-assignee', selected: issuable.assignee_id, project: @target_project, null_user: true, current_user: true, first_user: true)
 
   %div.prepend-top-default.clearfix
     .issuable-context-title