Use StandardCharsets class in user guide code examples, since it is more save than passing a string

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1610786 13f79535-47bb-0310-9956-ffa450edef68

Author: britter

src/site/xdoc/user-guide.xml

@@ -40,7 +40,7 @@ for (CSVRecord record : records) {
   </p>
   <source>final URL url = ...;
 try (
-    final Reader reader = new InputStreamReader(new BOMInputStream(url.openStream()), "UTF-8");
+    final Reader reader = new InputStreamReader(new BOMInputStream(url.openStream()), StandardCharsets.UTF_8);
     final CSVParser parser = new CSVParser(reader, CSVFormat.EXCEL.withHeader());
 ) {
     for (final CSVRecord record : parser) {