BlueSpire/Durandal — pull request #480 by petr-k (2014-04-15 19:16:11+00:00)
Title: Fixed DurandalRouteConfiguration.nav to be optional in Typescript definition

According to the [Router documentation](http://durandaljs.com/documentation/Using-The-Router.html) a route configuration object `nav` property is supposed to be optional. This fixes the Typescript definition file to accordingly.