Check for return types on setters (#122).

lib/src/rules.dart

Index: lib/src/rules.dart
diff --git a/lib/src/rules.dart b/lib/src/rules.dart
index 5d5a55efd5d6b8abad05d2e53ceca6d1585adda1..f20726ddb13078a9eb3650c0b160a8bfcdbcf5a9 100644
--- a/lib/src/rules.dart
+++ b/lib/src/rules.dart
@@ -12,6 +12,7 @@ import 'package:linter/src/rules/always_declare_return_types.dart';
 import 'package:linter/src/rules/always_specify_types.dart';
 import 'package:linter/src/rules/avoid_as.dart';
 import 'package:linter/src/rules/avoid_empty_else.dart';
+import 'package:linter/src/rules/avoid_return_types_on_setters.dart';
 import 'package:linter/src/rules/camel_case_types.dart';
 import 'package:linter/src/rules/constant_identifier_names.dart';
 import 'package:linter/src/rules/empty_constructor_bodies.dart';
@@ -36,6 +37,7 @@ final Registry ruleRegistry = new Registry()
   ..register(new AlwaysSpecifyTypes())
   ..register(new AvoidAs())
   ..register(new AvoidEmptyElse())
+  ..register(new AvoidReturnTypesOnSetters())
   ..register(new CamelCaseTypes())
   ..register(new ConstantIdentifierNames())
   ..register(new EmptyConstructorBodies())