update to new `package:github` API (#1841)

* update to new github API

* update
diff --git a/pubspec.yaml b/pubspec.yaml
index 0e07866..4c2d99b 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -26,7 +26,7 @@
   benchmark_harness: ^1.0.0
   cli_util: ^0.1.2
   dart_style: ^1.3.3
-  github: ^5.0.0
+  github: ^6.0.0
   grinder: ^0.8.0
   markdown: ^2.0.0
   matcher: ^0.12.0
diff --git a/tool/crawl.dart b/tool/crawl.dart
index a2bc1f2..dce566a 100644
--- a/tool/crawl.dart
+++ b/tool/crawl.dart
@@ -5,7 +5,7 @@
 import 'dart:io';
 
 import 'package:analyzer/src/lint/registry.dart';
-import 'package:github/server.dart';
+import 'package:github/github.dart';
 import 'package:http/http.dart' as http;
 import 'package:linter/src/analyzer.dart';
 import 'package:linter/src/rules.dart';
@@ -173,8 +173,8 @@
 }
 
 Future<List<String>> _fetchSdkTags() {
-  var github = createGitHubClient();
-  var slug = RepositorySlug('dart-lang', 'sdk');
+  final github = GitHub();
+  final slug = RepositorySlug('dart-lang', 'sdk');
 
   return github.repositories.listTags(slug).map((t) => t.name).where((t) {
     // Filter on numeric release tags.
diff --git a/tool/scorecard.dart b/tool/scorecard.dart
index 21226bf..467c848 100644
--- a/tool/scorecard.dart
+++ b/tool/scorecard.dart
@@ -7,8 +7,7 @@
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/src/lint/registry.dart';
-
-import 'package:github/server.dart';
+import 'package:github/github.dart';
 import 'package:http/http.dart' as http;
 import 'package:linter/src/analyzer.dart';
 import 'package:linter/src/rules.dart';
@@ -221,7 +220,7 @@
   }
 
   static Future<List<Issue>> _getIssues() async {
-    var github = createGitHubClient();
+    var github = GitHub();
     var slug = RepositorySlug('dart-lang', 'linter');
     return github.issues.listByRepo(slug).toList();
   }