fix compatibility with latest dart SDK

.travis.yml

@@ -0,0 +1,4 @@
+language: dart
+dart:
+  - stable
+  - dev

lib/extractor.dart

@@ -1,13 +1,13 @@
 /*
  * Copyright (c) 2018, Michael Mitterer (office@mikemitterer.at),
  * IT-Consulting and Development Limited.
- * 
+ *
  * All Rights Reserved.
- * 
+ *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *    http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software

lib/extractor/L10NMessageExtraction.dart

@@ -7,7 +7,7 @@
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *    http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
@@ -156,7 +156,7 @@ class L10NFindingVisitor extends GeneralizingAstVisitor {
         }
 
         // e.g. l10n("Test 2 - Plural Name: {name}",{ "name" : "Mike" });
-        if(arguments.length == 2 && arguments.last is! MapLiteral) {
+        if(arguments.length == 2 && arguments.last is! SetOrMapLiteral) {
             return false;
         }
 
@@ -191,7 +191,7 @@ class L10NFindingVisitor extends GeneralizingAstVisitor {
             _logger.shout("Unexpected exception: $e, $s");
             throw L10NMessageExtractionException("Unexpected exception: $e, $s");
         }
-        
+
         return false;
     }
 
@@ -208,7 +208,7 @@ class L10NFindingVisitor extends GeneralizingAstVisitor {
 
             final messageCode =
                 message.toOriginalCode(includeDesc: false, includeExamples: false);
-            
+
             if (existingCode != messageCode) {
                 extraction._makeWarning("WARNING: Duplicate message name:\n"
                     "'${message.name}' occurs more than once in ${extraction.origin}");

lib/l10n.dart

@@ -1,6 +1,7 @@
 library l10n;
 
-import "dart:collection";
+import 'dart:async';
+import 'dart:collection';
 import 'dart:convert';
 import 'package:intl/intl.dart';
 import 'package:intl/date_symbol_data_local.dart';
@@ -34,18 +35,18 @@ String tr(final String msgid, [final Map<String, dynamic> vars = const {} ]) {
 ///
 ///     // Include this if you run your app in the browser
 ///     import 'package:intl/intl_browser.dart';
-///     
+///
 ///     import 'package:l10n/l10n.dart';
 ///     import 'package:browser_example/_l10n/messages_all.dart';
-///     
+///
 ///     Future main() async {
 ///         final String locale = await initLanguageSettings(
 ///                 () => findSystemLocale(),
 ///                 (final String locale) => initializeMessages(locale)
 ///         );
 ///         ...
 ///     }
-///     
+///
 Future<String> initLanguageSettings(
     Future<String> findLocale(),
     Future<bool> initMessages(final String locale)) async {