Require Dart 2.14, prepare to release v0.13.4 (#626)

Removed unneeded utility function
diff --git a/.github/workflows/test-package.yml b/.github/workflows/test-package.yml
index cdc25d9..82602a8 100644
--- a/.github/workflows/test-package.yml
+++ b/.github/workflows/test-package.yml
@@ -47,7 +47,7 @@
       matrix:
         # Add macos-latest and/or windows-latest if relevant for this package.
         os: [ubuntu-latest]
-        sdk: [2.12.0, dev]
+        sdk: [2.14.0, dev]
     steps:
       - uses: actions/checkout@v2
       - uses: dart-lang/setup-dart@v1.0
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 08a3a0b..18fc78d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
-## 0.13.4-dev
+## 0.13.4
 
 * Throw a more useful error when a client is used after it has been closed.
+* Require Dart 2.14.
 
 ## 0.13.3
 
diff --git a/lib/src/browser_client.dart b/lib/src/browser_client.dart
index f41d0ba..b046b01 100644
--- a/lib/src/browser_client.dart
+++ b/lib/src/browser_client.dart
@@ -11,7 +11,6 @@
 import 'byte_stream.dart';
 import 'exception.dart';
 import 'streamed_response.dart';
-import 'utils.dart' show unawaited;
 
 /// Create a [BrowserClient].
 ///
diff --git a/lib/src/utils.dart b/lib/src/utils.dart
index f03ffb7..e79108e 100644
--- a/lib/src/utils.dart
+++ b/lib/src/utils.dart
@@ -74,6 +74,3 @@
       sink.close();
       onDone();
     }));
-
-// TODO: Remove after Dart 2.14 is stable
-void unawaited<T>(Future<T> future) {}
diff --git a/pubspec.yaml b/pubspec.yaml
index 1340d51..014fd31 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,10 +1,10 @@
 name: http
-version: 0.13.4-dev
+version: 0.13.4
 homepage: https://github.com/dart-lang/http
 description: A composable, multi-platform, Future-based API for HTTP requests.
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: '>=2.14.0 <3.0.0'
 
 dependencies:
   async: ^2.5.0
diff --git a/test/io/utils.dart b/test/io/utils.dart
index 5475f97..d2208fb 100644
--- a/test/io/utils.dart
+++ b/test/io/utils.dart
@@ -2,6 +2,7 @@
 // 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.
 
+import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
diff --git a/test/response_test.dart b/test/response_test.dart
index 22a926d..38061c1 100644
--- a/test/response_test.dart
+++ b/test/response_test.dart
@@ -5,7 +5,6 @@
 import 'dart:async';
 
 import 'package:http/http.dart' as http;
-import 'package:http/src/utils.dart' show unawaited;
 import 'package:test/test.dart';
 
 void main() {