Fix a variable name typo in yaml.

pkg/yaml/lib/src/constructor.dart

 // Copyright (c) 2012, 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 yaml.constructor;
 
 import 'equality.dart';
 import 'model.dart';
 import 'visitor.dart';
 import 'yaml_node.dart';
@@ skipping 35 matching lines @@
     var dartMap = setAnchor(map, new YamlMap(nodes, map.span));
     super.visitMapping(map).forEach((k, v) => nodes[k] = v);
     return dartMap;
   }
 
   /// Returns a new Dart object wrapping the object that already represents
   /// [anchored], if such a thing exists.
   YamlNode getAnchor(Node anchored) {
     if (anchored.anchor == null) return null;
     var value = _anchors[anchored.anchor];
-    if (vaule == null) return null;
+    if (value == null) return null;
 
     // Re-wrap [value]'s contents so that it's associated with the span of the
     // anchor rather than its original definition.
     if (value is YamlMap) return new YamlMap(value.nodes, anchored.span);
     if (value is YamlList) return new YamlList(value.nodes, anchored.span);
     assert(value is YamlScalar);
     return new YamlScalar(value.value, anchored.span);
   }
 
   /// Records that [value] is the Dart object representing [anchored].
   YamlNode setAnchor(Node anchored, YamlNode value) {
     if (anchored.anchor == null) return value;
     _anchors[anchored.anchor] = value;
     return value;
   }
 }