Use pub_semver package in pub.

sdk/lib/_internal/pub_generated/test/preprocess_test.dart

 library pub.test.preprocess_test;
+import 'package:pub_semver/pub_semver.dart';
 import 'package:unittest/unittest.dart';
 import '../lib/src/preprocess.dart';
-import '../lib/src/version.dart';
 import 'test_pub.dart';
 main() {
   initConfig();
   test("does nothing on a file without preprocessor directives", () {
     var text = '''
 some text
 // normal comment
 // #
  //# not beginning of line
 ''';
@@ skipping 246 matching lines @@
 //# else barback <0.5.0
 //# end
 '''), throwsFormatException);
       });
     });
   });
 }
 String _preprocess(String input) => preprocess(input, {
   'barback': new Version.parse("1.2.3")
 }, 'source/url');