Remove unused dart:async import

.travis.yml

@@ -1,7 +1,7 @@
 language: dart
 
 dart:
-  - 2.0.0
+  - 2.1.0
   - dev
 
 dart_task:

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.0.6
+
+* Require Dart >=2.1
+
 ## 1.0.5
 
 * Don't allow the test to time out as long as the process is emitting output.

pubspec.yaml

@@ -1,11 +1,11 @@
 name: test_process
-version: 1.0.5
+version: 1.0.6-dev
 
 description: A package for testing subprocesses.
 homepage: https://github.com/dart-lang/test_process
 
 environment:
-  sdk: '>=2.0.0 <3.0.0'
+  sdk: '>=2.1.0 <3.0.0'
 
 dependencies:
   async: ^2.0.0

test/test_process_test.dart

@@ -2,7 +2,6 @@
 // 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:io';
 
 import 'package:path/path.dart' as p;