use green bg for merged MR badge

app/assets/stylesheets/common.scss

@@ -195,6 +195,11 @@ p.time {
   top: -5px;
   @include border-radius(4px);
+  &.success {
+    background: #4A4;
+    color: #FFF;
+  }
+
   &.error {
     background: #DA4E49;
     color: #FFF;

app/views/merge_requests/show/_mr_box.html.haml

@@ -3,7 +3,7 @@
     %h4.box-title
       = gfm escape_once(@merge_request.title)
       - if @merge_request.merged?
-        .error.status_info
+        .success.status_info
           %i.icon-ok
           Merged
       - elsif @merge_request.closed?