Merge branch 'fix-diff-system-note-alignment' into 'master'

Fix system note alignment within diff

See merge request gitlab-org/gitlab-ce!29446

app/assets/stylesheets/pages/notes.scss

@@ -431,7 +431,7 @@ $note-form-margin-left: 72px;
 
   .notes > .note-discussion li.note.system-note {
     border-bottom: 0;
-    padding: 0 $gl-padding;
+    padding: 0;
   }
 }