Added two properties to set qrWidth and qrHeight in web apps

Author: massmarz

lib/simple_barcode_scanner.dart

@@ -25,7 +25,7 @@ class SimpleBarcodeScannerPage extends StatelessWidget {
   ///center Title
   final bool? centerTitle;
 
-  /// Only for web app, set qrBox width and height
+  /// Only for web apps, set qrBox width and height
   final int scanWidth;
   final int scanHeight;