Use warning color merge conflicts icon in MR status widget.

app/assets/stylesheets/pages/merge_requests.scss

@@ -105,6 +105,11 @@
       font-size: 17px;
       margin: 5px 0;
       color: $gl-gray-dark;
+
+      &.has-conflicts .fa-exclamation-triangle {
+        color: $gl-warning;
+      }
+
     }
 
     p:last-child {

app/views/projects/merge_requests/widget/open/_conflicts.html.haml

-%h4
+%h4.has-conflicts
   = icon("exclamation-triangle")
   This merge request contains merge conflicts
 
 %p
-  Please resolve these conflicts or 
+  Please resolve these conflicts or
   - if @merge_request.can_be_merged_by?(current_user)
     #{link_to "merge this request manually", "#modal_merge_info", class: "how_to_merge_link vlink", "data-toggle" => "modal"}.
   - else