Fix dart:io constants (#26)

* Fix dart:io constants
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 89443ba..1461109 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 2.0.1
+
+* Use lower-case constants from dart:io.
+
 ## 2.0.0
 
 * Make port functions generic so they can be used in a Dart 2 type-safe way.
diff --git a/example/http_server.dart b/example/http_server.dart
index 0f6f30e..a9ee97b 100644
--- a/example/http_server.dart
+++ b/example/http_server.dart
@@ -26,7 +26,7 @@
   HttpListener listener = args[1];
 
   var server =
-      await HttpServer.bind(InternetAddress.ANY_IP_V6, port, shared: true);
+      await HttpServer.bind(InternetAddress.anyIpV6, port, shared: true);
   await listener.start(server);
 
   return singleCallbackPort((SendPort resultPort) {
@@ -90,7 +90,7 @@
   // Used to ensure the requested port is available or to find an available
   // port if `0` is provided.
   ServerSocket socket =
-      await ServerSocket.bind(InternetAddress.ANY_IP_V6, port, shared: true);
+      await ServerSocket.bind(InternetAddress.anyIpV6, port, shared: true);
 
   port = socket.port;
   var isolates = await Future
diff --git a/pubspec.yaml b/pubspec.yaml
index a2b7aab..c0a946a 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,9 +1,9 @@
 name: isolate
-version: 2.0.0
+version: 2.0.1
 author: Dart Team <misc@dartlang.org>
 description: Utility functions and classes related to the 'dart:isolate' library.
 homepage: https://github.com/dart-lang/isolate
 environment:
-  sdk: '>=2.0.0-dev.20.0 <2.0.0'
+  sdk: '>=2.0.0-dev.55.0 <2.0.0'
 dev_dependencies:
   test: '^0.12.0'