upgrade xml package

lib/domain/atom_feed.dart

@@ -40,7 +40,7 @@ class AtomFeed {
   });
 
   factory AtomFeed.parse(String xmlString) {
-    var document = parse(xmlString);
+    var document = XmlDocument.parse(xmlString);
     XmlElement feedElement;
     try {
       feedElement = document.findElements("feed").first;

lib/domain/rss_feed.dart

@@ -59,7 +59,7 @@ class RssFeed {
   });
 
   factory RssFeed.parse(String xmlString) {
-    var document = parse(xmlString);
+    var document = XmlDocument.parse(xmlString);
     XmlElement channelElement;
     try {
       channelElement = document.findAllElements("channel").first;

pubspec.yaml

@@ -6,7 +6,7 @@ homepage: https://github.com/witochandra/webfeed
 environment:
   sdk: ">=2.0.0 <3.0.0"
 dependencies:
-  xml: "^3.0.0"
+  xml: "^4.3.0"
   intl: "^0.16.0"
 dev_dependencies:
   test: ^1.3.0