Fix all strong-mode warnings.

lib/src/equality.dart

 // Copyright (c) 2014, 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.
 
 import 'dart:collection';
 
 import 'package:collection/collection.dart';
 
 import 'yaml_node.dart';
 
 /// Returns a [Map] that compares its keys based on [deepEquals].
-Map deepEqualsMap() => new HashMap(equals: deepEquals, hashCode: deepHashCode);
+Map/*<K, V>*/ deepEqualsMap/*<K, V>*/() =>
+    new HashMap(equals: deepEquals, hashCode: deepHashCode);
 
 /// Returns whether two objects are structurally equivalent.
 ///
 /// This considers `NaN` values to be equivalent, handles self-referential
 /// structures, and considers [YamlScalar]s to be equal to their values.
 bool deepEquals(obj1, obj2) => new _DeepEquals().equals(obj1, obj2);
 
 /// A class that provides access to the list of parent objects used for loop
 /// detection.
 class _DeepEquals {
@@ skipping 92 matching lines @@
       } else {
         return value.hashCode;
       }
     } finally {
       parents.removeLast();
     }
   }
 
   return _deepHashCode(obj);
 }