CmdCalendar: Properly colorize overdue task from today

Even if task is due today, but the due time is in the past, it is
considered overdue according to the implementation of Task::is_overdue
method.

Make coloring in the calendar output consistent.

src/commands/CmdCalendar.cpp

@@ -582,11 +582,11 @@ std::string CmdCalendar::renderMonths (
                   cellColor.blend (color_due);
                   break;
 
-                case Task::dateEarlierToday:
                 case Task::dateLaterToday:
                   cellColor.blend (color_duetoday);
                   break;
 
+                case Task::dateEarlierToday:
                 case Task::dateBeforeToday:
                   cellColor.blend (color_overdue);
                   break;