Add @override annotations to flutter framework

packages/flutter_tools/lib/src/runner/flutter_command.dart

diff --git a/packages/flutter_tools/lib/src/runner/flutter_command.dart b/packages/flutter_tools/lib/src/runner/flutter_command.dart
index b763f8e..d20c7b2 100644
--- a/packages/flutter_tools/lib/src/runner/flutter_command.dart
+++ b/packages/flutter_tools/lib/src/runner/flutter_command.dart
@@ -18,6 +18,7 @@
 typedef bool Validator();
 
 abstract class FlutterCommand extends Command {
+  @override
   FlutterCommandRunner get runner => super.runner;
 
   /// Whether this command needs to be run from the root of a project.
@@ -43,6 +44,7 @@
     applicationPackages ??= await ApplicationPackageStore.forConfigs(buildConfigurations);
   }
 
+  @override
   Future<int> run() {
     Stopwatch stopwatch = new Stopwatch()..start();