Add missing reference to knockout.mapping definitions

knockout.mapping/knockout.mapping-2.0.d.ts

@@ -3,6 +3,8 @@
 // Definitions by: Boris Yankov <https://github.com/borisyankov/>
 // Definitions https://github.com/borisyankov/DefinitelyTyped
 
+/// <reference path="../knockout/knockout-2.2.d.ts" />
+
 interface KnockoutMappingCreateOptions {
     data: any;
     parent: any;