Lint rule: Do not override fields.

lib/src/rules.dart

Index: lib/src/rules.dart
diff --git a/lib/src/rules.dart b/lib/src/rules.dart
index 7f18028470d41a2c7fa6a0504c6d26de92ae9c8d..6a2f2e33c9a3df954b4fc35ad2a5c8ef6335146a 100644
--- a/lib/src/rules.dart
+++ b/lib/src/rules.dart
@@ -18,6 +18,7 @@ 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';
+import 'package:linter/src/rules/final_override_non_final.dart';
 import 'package:linter/src/rules/hash_and_equals.dart';
 import 'package:linter/src/rules/implementation_imports.dart';
 import 'package:linter/src/rules/library_names.dart';
@@ -49,6 +50,7 @@ final Registry ruleRegistry = new Registry()
   ..register(new CamelCaseTypes())
   ..register(new ConstantIdentifierNames())
   ..register(new EmptyConstructorBodies())
+  ..register(new FinalOverrideNonFinal())
   ..register(new HashAndEquals())
   ..register(new ImplementationImports())
   ..register(new LibraryNames())