Null operator on Chinese README

@@ -73,7 +73,7 @@ class MyApp extends StatelessWidget {
               return MediaQuery(
                 //Setting font does not change with system font size
                 data: MediaQuery.of(context).copyWith(textScaleFactor: 1.0),
-                child: widget,
+                child: widget!,
               );
             },
             theme: ThemeData(