Use pub_semver package in pub.

sdk/lib/_internal/pub/test/implicit_dependency_test.dart

Index: sdk/lib/_internal/pub/test/implicit_dependency_test.dart
diff --git a/sdk/lib/_internal/pub/test/implicit_dependency_test.dart b/sdk/lib/_internal/pub/test/implicit_dependency_test.dart
index 34e133f8d1ecc4cd88642f80e84e9dd66a253281..0a6756679ac7a07f6496086b16de2dcd879c2575 100644
--- a/sdk/lib/_internal/pub/test/implicit_dependency_test.dart
+++ b/sdk/lib/_internal/pub/test/implicit_dependency_test.dart
@@ -2,10 +2,11 @@
 // 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:pub_semver/pub_semver.dart';
+
 import 'descriptor.dart' as d;
 import 'test_pub.dart';
 import '../lib/src/barback.dart' as barback;
-import '../lib/src/version.dart';
 
 main() {
   initConfig();