fixes dart-archive#232

Widen constraint on code_transformers and use test utils from transformer_test package where they were migrated to from code_transformers.

pubspec.yaml

@@ -13,12 +13,13 @@ environment:
 dependencies:
   analyzer: '>=0.27.1 <0.28.0'
   barback: '>=0.15.0 <0.16.0'
-  code_transformers: '>=0.3.1 <0.4.0'
+  code_transformers: '>=0.3.1 <0.5.0'
   path: ">=1.3.0 <2.0.0"
 dev_dependencies:
   benchmark_harness: ">=1.0.4 <2.0.0"
   guinness2: '>=0.0.3 <1.0.0'
   matcher: '>=0.11.0 <0.13.0'
   test: '>=0.12.7 <0.13.0'
+  transformer_test: '^0.2.0'
 transformers:
 - di/module_transformer

test/transformer_test.dart

@@ -4,7 +4,7 @@ import 'dart:async';
 
 import 'package:barback/barback.dart';
 import 'package:code_transformers/resolver.dart';
-import 'package:code_transformers/tests.dart' as tests;
+import 'package:transformer_test/utils.dart' as tests;
 import 'package:di/transformer.dart';
 import 'package:di/transformer/options.dart';
 import 'package:di/transformer/injector_generator.dart';