Fix copyright date in new test

TBR=johnniwinther@google.com

Change-Id: I36f3366ecd64dff247a1f94f5caa2714fefb3a09
Reviewed-on: https://dart-review.googlesource.com/76704
Reviewed-by: Stephen Adams <sra@google.com>
Commit-Queue: Stephen Adams <sra@google.com>

tests/compiler/dart2js/codegen/pragma_annotations_test.dart

@@ -1,4 +1,4 @@
-// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2018, 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.