Fix bug where notes were being rendered with wrong color preferences due to caching

Closes #2008

app/views/projects/notes/_note.html.haml

@@ -56,7 +56,7 @@
       .note-body{class: note_editable?(note) ? 'js-task-list-container' : ''}
-        = cache [note, 'markdown'] do
+        = cache [note, 'markdown', user_color_scheme_class] do
           .note-text
             = preserve do
               = markdown(note.note, {no_header_anchors: true})