fixed value reset error in add_cam

lib/screens/excursion/widgets/tracking.dart

@@ -215,7 +215,7 @@ class _TrackingState extends State<Tracking> {
                     currentPosition!.longitude,
                   ),
                   radius: currentPosition!.accuracy,
-                  color: Colors.blue.withAlpha(2),
+                  color: Colors.blue.withOpacity(0.2),
                   borderColor: Colors.blue,
                   borderStrokeWidth: 2,
                 ),