Fix newly enforced lint (dart-archive/io#76)

Author: kevmoo

pkgs/io/test/shell_words_test.dart

@@ -2,9 +2,8 @@
 // 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 'package:test/test.dart';
-
 import 'package:io/io.dart';
+import 'package:test/test.dart';
 
 void main() {
   group('shellSplit()', () {