Fix recently introduced strong-mode errors

pkg/analysis_server/test/services/refactoring/move_file_test.dart

Index: pkg/analysis_server/test/services/refactoring/move_file_test.dart
diff --git a/pkg/analysis_server/test/services/refactoring/move_file_test.dart b/pkg/analysis_server/test/services/refactoring/move_file_test.dart
index 9146b93597e065d1930b36258c524ea4dbc5a4ce..df2e4221c2c016452c26a6acd76b182a47852f1e 100644
--- a/pkg/analysis_server/test/services/refactoring/move_file_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/move_file_test.dart
@@ -111,7 +111,7 @@ import '22/new_name.dart';
     testFile = '/packages/my_pkg/lib/aaa/test.dart';
     provider.newFile(testFile, '');
     Map<String, List<Folder>> packageMap = {
-      'my_pkg': [provider.getResource('/packages/my_pkg/lib')]
+      'my_pkg': <Folder>[provider.getResource('/packages/my_pkg/lib')]
     };
     context.sourceFactory = new SourceFactory([
       AbstractContextTest.SDK_RESOLVER,
@@ -243,7 +243,7 @@ export 'package:testName/myLib.dart';
     context.sourceFactory = new SourceFactory([
       AbstractContextTest.SDK_RESOLVER,
       new PackageMapUriResolver(provider, <String, List<Folder>>{
-        'testName': [provider.getResource('/testName/lib')]
+        'testName': <Folder>[provider.getResource('/testName/lib')]
       }),
       resourceResolver,
     ]);