Doc: update connect syntax digitalclock example

Task-number: QTBUG-60635
Change-Id: I9d8411b639e5cf74c9cb03de4b5f6081bb549151
Reviewed-by: Venugopal Shivashankar <Venugopal.Shivashankar@qt.io>

examples/widgets/widgets/digitalclock/digitalclock.cpp

@@ -59,7 +59,7 @@ DigitalClock::DigitalClock(QWidget *parent)
     setSegmentStyle(Filled);
 
     QTimer *timer = new QTimer(this);
-    connect(timer, SIGNAL(timeout()), this, SLOT(showTime()));
+    connect(timer, &QTimer::timeout, this, &DigitalClock::showTime);
     timer->start(1000);
 
     showTime();