Clarify presentation of the target in retaining paths.

runtime/observatory/lib/src/elements/code_view.dart

 // Copyright (c) 2013, 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.
 
 library code_view_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:observatory/cpu_profile.dart';
 import 'package:observatory/service.dart' as S;
@@ skipping 626 matching lines @@
         return 'dart';
       case M.CodeKind.native:
         return 'native';
       case M.CodeKind.stub:
         return 'stub';
       case M.CodeKind.tag:
         return 'tag';
       case M.CodeKind.collected:
         return 'collected';
     }
-    throw new Exception('Unkown CodeKind ($kind)');
+    throw new Exception('Unknown CodeKind ($kind)');
   }
 }