Fix deprecated StringBuffer usages in Intl

pkg/intl/lib/date_format.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of intl;
 
 // TODO(efortuna): Customized pattern system -- suggested by i18n needs
 // feedback on appropriateness.
 /**
  * DateFormat is for formatting and parsing dates in a locale-sensitive
@@ skipping 207 matching lines @@
     addPattern(newPattern);
   }
 
   /**
    * Return a string representing [date] formatted according to our locale
    * and internal format.
    */
   String format(DateTime date) {
     // TODO(efortuna): read optional TimeZone argument (or similar)?
     var result = new StringBuffer();
-    _formatFields.forEach((field) => result.add(field.format(date)));
+    _formatFields.forEach((field) => result.write(field.format(date)));
     return result.toString();
   }
 
   /**
    * Returns a date string indicating how long ago (3 hours, 2 minutes)
    * something has happened or how long in the future something will happen
    * given a [reference] DateTime relative to the current time.
    */
   String formatDuration(DateTime reference) {
     return '';
@@ skipping 350 matching lines @@
   List _reverse(List list) {
     // TODO(alanknight): Use standardized list reverse when implemented.
     // See Issue 2804.
     var result = new List();
     for (var i = list.length-1; i >= 0; i--) {
       result.addLast(list[i]);
     }
     return result;
   }
 }