Fix lingering references to the old Span in yaml.

pkg/yaml/lib/src/yaml_node.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.yaml_node;
 
 import 'dart:collection' as collection;
 
 import 'package:collection/collection.dart';
 import 'package:source_span/source_span.dart';
@@ skipping 99 matching lines @@
   /// [sourceUrl] may be either a [String], a [Uri], or `null`.
   factory YamlList({sourceUrl}) =>
       new YamlListWrapper(const [], sourceUrl);
 
   /// Wraps a Dart list so that it can be accessed (recursively) like a
   /// [YamlList].
   ///
   /// Any [SourceSpan]s returned by this list or its children will be dummies
   /// without useful location information. However, they will have a reasonable
   /// implementation of [SourceSpan.getLocationMessage]. If [sourceUrl] is
-  /// passed, it's used as the [Span.sourceUrl].
+  /// passed, it's used as the [SourceSpan.sourceUrl].
   ///
   /// [sourceUrl] may be either a [String], a [Uri], or `null`.
   factory YamlList.wrap(List dartList, {sourceUrl}) =>
       new YamlListWrapper(dartList, sourceUrl);
 
   /// Users of the library should not use this constructor.
   YamlList.internal(List<YamlNode> nodes, this.span)
       : nodes = new UnmodifiableListView<YamlNode>(nodes);
 
   operator [](int index) => nodes[index].value;
 
   operator []=(int index, value) {
     throw new UnsupportedError("Cannot modify an unmodifiable List");
   }
 }
 
 /// A wrapped scalar value parsed from YAML.
 class YamlScalar extends YamlNode {
   final SourceSpan span;
 
   final value;
 
   /// Wraps a Dart value in a [YamlScalar].
   ///
   /// This scalar's [span] won't have useful location information. However, it
   /// will have a reasonable implementation of [SourceSpan.message]. If
-  /// [sourceUrl] is passed, it's used as the [Span.sourceUrl].
+  /// [sourceUrl] is passed, it's used as the [SourceSpan.sourceUrl].
   ///
   /// [sourceUrl] may be either a [String], a [Uri], or `null`.
   YamlScalar.wrap(this.value, {sourceUrl})
       : span = new NullSpan(sourceUrl);
 
   /// Users of the library should not use this constructor.
   YamlScalar.internal(this.value, this.span);
 
   String toString() => value.toString();
 }