enhance example

example/main.dart

@@ -1,24 +1,19 @@
 import 'package:http/http.dart' as http;
 import 'package:webfeed/webfeed.dart';
 
-void main() {
-  var client = new http.Client();
+void main() async {
+  var client = http.Client();
 
   // RSS feed
-  client.get("https://developer.apple.com/news/releases/rss/releases.rss").then((response) {
-    return response.body;
-  }).then((bodyString) {
-    var channel = new RssFeed.parse(bodyString);
-    print(channel);
-    return channel;
-  });
+  var response = await client
+      .get("https://developer.apple.com/news/releases/rss/releases.rss");
+  var channel = RssFeed.parse(response.body);
+  print(channel);
 
   // Atom feed
-  client.get("https://www.theverge.com/rss/index.xml").then((response) {
-    return response.body;
-  }).then((bodyString) {
-    var feed = new AtomFeed.parse(bodyString);
-    print(feed);
-    return feed;
-  });
+  response = await client.get("https://www.theverge.com/rss/index.xml");
+  var feed = AtomFeed.parse(response.body);
+  print(feed);
+
+  client.close();
 }