unittest: fix library name for prints matcher

test/prints_matcher_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
-library matcher.prints_matchers_test;
+library unittest.prints_matchers_test;
 
 import 'dart:async';
 
 import 'package:metatest/metatest.dart';
 import 'package:unittest/unittest.dart';
 
 /// The VM and dart2js have different toStrings for closures.
 final closureToString = (() {}).toString();
 
 void main() => initTests(_test);
@@ skipping 119 matching lines @@
 ''')
     },
     {
       'result': 'fail',
       'message': startsWith(r'''Expected future to complete successfully, but it failed with Expected: contains 'Goodbye'
   Actual: ''
 ''')
     }
   ]);
 }