Use APIs from the latest collection package.

lib/src/runner/configuration.dart

Index: lib/src/runner/configuration.dart
diff --git a/lib/src/runner/configuration.dart b/lib/src/runner/configuration.dart
index c7dbb574c4992700c51b0a6fa230ab6187de116d..546310c63c3245a5c286722da8ee8c46a0755c79 100644
--- a/lib/src/runner/configuration.dart
+++ b/lib/src/runner/configuration.dart
@@ -5,7 +5,7 @@
 import 'dart:io';
 
 import 'package:boolean_selector/boolean_selector.dart';
-import 'package:collection/collection.dart' hide mapMap, mergeMaps;
+import 'package:collection/collection.dart';
 import 'package:glob/glob.dart';
 import 'package:path/path.dart' as p;
 
@@ -14,7 +14,6 @@ import '../backend/platform_selector.dart';
 import '../backend/test_platform.dart';
 import '../frontend/timeout.dart';
 import '../util/io.dart';
-import '../utils.dart';
 import 'configuration/args.dart' as args;
 import 'configuration/load.dart';
 import 'configuration/values.dart';