Modernize the package's style.

test/unmodifiable_collection_test.dart

Index: test/unmodifiable_collection_test.dart
diff --git a/test/unmodifiable_collection_test.dart b/test/unmodifiable_collection_test.dart
index 6c722d090c15ce028c8efd42ce26d8daaeb2cd71..682a40609d32c3831662ef39c932c7dc850b6e9c 100644
--- a/test/unmodifiable_collection_test.dart
+++ b/test/unmodifiable_collection_test.dart
@@ -2,9 +2,10 @@
 // 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:collection/wrappers.dart";
 import "package:test/test.dart";
 
+import "package:collection/collection.dart";
+
 // Test unmodifiable collection views.
 // The collections should pass through the operations that are allowed,
 // an throw on the ones that aren't without affecting the original.