analyzer fixes and package updates

Author: lohanidamodar

templates/dart/lib/package.dart.twig

@@ -2,14 +2,12 @@ library {{ language.params.packageName }};
 
 import 'dart:async';
 import 'dart:typed_data';
-import 'package:http/http.dart' show MultipartFile;
 import 'src/enums.dart';
 import 'src/client.dart';
 import 'src/service.dart';
 import 'src/input_file.dart';
 import 'src/upload_progress.dart';
 import 'models.dart' as models;
-import 'src/exception.dart';
 
 export 'src/response.dart';
 export 'src/client.dart';

templates/dart/lib/src/client.dart.twig

@@ -3,7 +3,6 @@ import 'client_stub.dart'
     if (dart.library.html) 'client_browser.dart'
     if (dart.library.io) 'client_io.dart';
 import 'response.dart';
-import 'input_file.dart';
 import 'upload_progress.dart';
 
 abstract class Client {

templates/dart/pubspec.yaml.twig

@@ -12,4 +12,4 @@ dependencies:
 
 dev_dependencies:
   test: ^1.16.8
-  lints: ^1.0.1
+  lints: ^2.0.0