issue rhymelph#62 fix

Error:

/C:/Users/FaazLaeeq/AppData/Local/Pub/Cache/hosted/pub.dev/r_scan-0.1.6+1/lib/src/r_scan_view.dart:38:18: Error: Member not found: 'SystemChrome.setEnabledSystemUIOverlays'.
    SystemChrome.setEnabledSystemUIOverlays([SystemUiOverlay.top]);
    
Solution:

change line 38 from this:
    SystemChrome.setEnabledSystemUIOverlays([SystemUiOverlay.top]);
to this:
SystemChrome.setEnabledSystemUIMode(SystemUiMode.manual,
        overlays: [SystemUiOverlay.top]);

lib/src/r_scan_view.dart

@@ -35,7 +35,8 @@ class _RScanViewState extends State<RScanView> {
   void initState() {
     super.initState();
     _controller = widget.controller;
-    SystemChrome.setEnabledSystemUIOverlays([SystemUiOverlay.top]);
+SystemChrome.setEnabledSystemUIMode(SystemUiMode.manual,
+        overlays: [SystemUiOverlay.top]);
   }
 
   @override