Update invalid package name example

pkg/compiler/lib/src/warnings.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js;
 
 const DONT_KNOW_HOW_TO_FIX = "Computer says no!";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 1599 matching lines @@
 // can't have a 'top level' package URI
 import 'package:foo.dart';
 
 main() {}
 """, """
 // can't have 2 slashes
 import 'package://foo/foo.dart';
 
 main() {}
 """, """
-// package name must be a valid identifier
-import 'package:not-valid/foo.dart';
+// package name must be valid
+import 'package:not\valid/foo.dart';
 
 main() {}
 """]);
 
   static const MessageKind READ_SCRIPT_ERROR = const MessageKind(
       "Can't read '#{uri}' (#{exception}).",
       // Don't know how to fix since the underlying error is unknown.
       howToFix: DONT_KNOW_HOW_TO_FIX,
       examples: const [
           """
@@ skipping 980 matching lines @@
   static String convertToString(value) {
     if (value is ErrorToken) {
       // Shouldn't happen.
       return value.assertionMessage;
     } else if (value is Token) {
       value = value.value;
     }
     return '$value';
   }
 }