Fix URL for rules JSON file source

The site-wwww repo renamed the `_data` directory to `data`.
Refactor to a URI for better formatting.

Author: natebosch

pkgs/lints/tool/gen_docs.dart

@@ -10,8 +10,10 @@ import 'package:yaml/yaml.dart' as yaml;
 import 'package:http/http.dart' as http;
 
 /// Source of truth for linter rules.
-const rulesUrl =
-    'https://raw.githubusercontent.com/dart-lang/site-www/main/src/_data/linter_rules.json';
+final rulesUri = Uri.https(
+  'raw.githubusercontent.com',
+  'dart-lang/site-www/main/src/data/linter_rules.json',
+);
 
 /// Local cache of linter rules from [rulesUrl].
 ///
@@ -91,7 +93,7 @@ Future<Map<String, Map<String, String>>> _fetchRulesJson({
     final rulesJsonText = rulesJsonFile.readAsStringSync();
     return _readJson(rulesJsonText);
   }
-  final rulesJsonText = (await http.get(Uri.parse(rulesUrl))).body;
+  final rulesJsonText = (await http.get(rulesUri)).body;
   final rulesJson = _readJson(rulesJsonText);
 
   // Re-save [rulesJsonFile] file.