Update signatures for implementation of Iterable.singleWhere (#63)

* Update signatures for implementation of Iterable.singleWhere

* Add an check if orElse is passed in

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 50deb7f..0292123 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 0.13.2+2
+
+* Update signature for implementations of `Iterable.singleWhere` to include 
+  optional argument.
+   
 ## 0.13.2+1
 
 * Changed the implementation of `Set` and `List` classes to use base classes

lib/dom.dart

diff --git a/lib/dom.dart b/lib/dom.dart
index fb0d458..df9655e 100644
--- a/lib/dom.dart
+++ b/lib/dom.dart
@@ -951,7 +951,8 @@
     return _filtered.lastWhere(test, orElse: orElse);
   }
 
-  Element singleWhere(bool test(Element value)) {
+  Element singleWhere(bool test(Element value), {Element orElse()}) {
+    if (orElse != null) throw new UnimplementedError('orElse');
     return _filtered.singleWhere(test);
   }
 

pubspec.yaml

diff --git a/pubspec.yaml b/pubspec.yaml
index acbe3f6..59f1650 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: html
-version: 0.13.2+1
+version: 0.13.2+2
 author: Dart Team <misc@dartlang.org>
 description: A library for working with HTML documents. Previously known as html5lib.
 homepage: https://github.com/dart-lang/html