Pass a URI to package:http API

Updates example to be forwards compatible with the breaking change in
dart-lang/http#507

Author: natebosch

src/docs/cookbook/networking/fetch-data.md

@@ -242,7 +242,7 @@ import 'package:http/http.dart' as http;
 
 Future<Album> fetchAlbum() async {
   final response =
-      await http.get('https://jsonplaceholder.typicode.com/albums/1');
+      await http.get(Uri.https('jsonplaceholder.typicode.com', 'albums/1');
 
   if (response.statusCode == 200) {
     // If the server did return a 200 OK response,