add test in rss author

test/rss_test.dart

@@ -21,6 +21,7 @@ void main() {
     expect(feed.title, "News - Foo bar News");
     expect(feed.description, "Foo bar News and Updates feed provided by Foo bar, Inc.");
     expect(feed.link, "https://foo.bar.news/");
+    expect(feed.author, "hello@world.net");
     expect(feed.language, "en-US");
     expect(feed.lastBuildDate, "Mon, 26 Mar 2018 14:00:00 PDT");
     expect(feed.generator, "Custom");

test/xml/RSS.xml

@@ -5,6 +5,7 @@
     <channel>
         <title>News - Foo bar News</title>
         <link>https://foo.bar.news/</link>
+        <author>hello@world.net</author>
         <description>Foo bar News and Updates feed provided by Foo bar, Inc.</description>
         <image>
             <url>https://foo.bar.news/logo.gif</url>