fix deprecation

Author: kevmoo

pubspec.yaml

@@ -1,5 +1,5 @@
 name: source_gen
-version: 0.4.8
+version: 0.4.9-dev
 author: Dart Team <[email protected]>
 description: Automatic sourcecode generation for Dart
 homepage: https://github.com/dart-lang/source_gen

test/test_files/json_test_example.dart

@@ -6,7 +6,7 @@ library source_gen.test.example;
 
 import 'dart:collection';
 
-import 'package:collection/equality.dart';
+import 'package:collection/collection.dart';
 import 'package:source_gen/generators/json_serializable.dart';
 
 part 'json_test_example.g.dart';