Convert from unittest to test

R=scheglov@google.com

Review URL: https://codereview.chromium.org//2320213003 .

pubspec.yaml

diff --git a/pubspec.yaml b/pubspec.yaml
index 92f0932..dfe777a 100755
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -6,4 +6,4 @@
 environment:
   sdk: '>=1.0.0 <2.0.0'
 dev_dependencies:
-  unittest: any
+  test: any

test/plugin_impl_test.dart

diff --git a/test/plugin_impl_test.dart b/test/plugin_impl_test.dart
index c8603af..2221cf8 100644
--- a/test/plugin_impl_test.dart
+++ b/test/plugin_impl_test.dart
@@ -6,11 +6,9 @@
 
 import 'package:plugin/plugin.dart';
 import 'package:plugin/src/plugin_impl.dart';
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 main() {
-  groupSep = ' | ';
-
   group('ExtensionManager', () {
     test('processPlugins', () {
       TestPlugin plugin1 = new TestPlugin('plugin1');