Minor Dart 2 changes for Intl

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=189839254
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8ed4b8e..3dbf1bd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+## 0.15.4
+ * A couple of minor Dart 2 fixes.
+
 ## 0.15.3
  * Add a customPattern parameter to the currency constructor. This can be used
    to provide a custom pattern if you have one, e.g. for accounting formats.
diff --git a/lib/intl.dart b/lib/intl.dart
index 6f4e01b..b1f1de8 100644
--- a/lib/intl.dart
+++ b/lib/intl.dart
@@ -477,7 +477,7 @@
 
   /// Internal: Implements the logic for select - use [select] for
   /// normal messages.
-  static selectLogic(Object choice, Map<String, String> cases) {
+  static selectLogic(Object choice, Map<String, dynamic> cases) {
     // Allow passing non-strings, e.g. enums to a select.
     choice = "$choice";
     var exact = cases[choice];
diff --git a/lib/message_lookup_by_library.dart b/lib/message_lookup_by_library.dart
index 48973fb..5b376e5 100644
--- a/lib/message_lookup_by_library.dart
+++ b/lib/message_lookup_by_library.dart
@@ -131,8 +131,9 @@
   operator [](String messageName) => messages[messageName];
 
   /// Subclasses should override this to return a list of their message
-  /// functions.
-  Map<String, Function> get messages;
+  /// implementations. In this class these are functions, but subclasses may
+  /// implement them differently.
+  Map<String, dynamic> get messages;
 
   /// Subclasses should override this to return their locale, e.g. 'en_US'
   String get localeName;
diff --git a/pubspec.yaml b/pubspec.yaml
index b94ed7e..fd661ca 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: intl
-version: 0.15.3
+version: 0.15.4
 author: Dart Team <misc@dartlang.org>
 description: Contains code to deal with internationalized/localized messages, date and number formatting and parsing, bi-directional text, and other internationalization issues.
 homepage: https://github.com/dart-lang/intl