Update lint_rule.dart (#259)

only show AnalysisError from package:analyzer/error/error.dart

Author: David Wimmer

packages/custom_lint_core/lib/src/lint_rule.dart

@@ -4,7 +4,7 @@ import 'dart:io';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/utilities.dart';
 import 'package:analyzer/dart/ast/ast.dart';
-import 'package:analyzer/error/error.dart';
+import 'package:analyzer/error/error.dart' show AnalysisError;
 import 'package:analyzer/error/listener.dart';
 import 'package:meta/meta.dart';
 import 'package:pubspec_parse/pubspec_parse.dart';